Saturday, December 12, 2009

Leopards and Chanukah

For an audio shiur on leopards and Chanukah, click here, and scroll down to "Zoology and Torah (Part 3), December 6, 2009." It's just 99 cents. Here's the accompanying YouTube clip:

Monday, November 16, 2009

Help a Lonely Iguana with a Shidduch!

Several readers of this blog live in Ramat Bet Shemesh and enjoy looking at all the animals in my Pinat Chai. Everyone's favorite animal is Mary Jane, my large iguana. She's a magnificent creature, but somewhat lonely. Large male iguanas are hard to come by, but right now somebody in Israel is selling one, five feet long, for $130. However, my wife has pointed out to me that I have already exceeded my animal-buying budget for this year and about 150 years into the future. So, if any readers would like to watch a huge male iguana cavorting around my garden and swimming in the pond, please feel free to donate via the link below! No donation is too small!

Thursday, November 5, 2009

Live Internet Classes - Free!

I am thrilled to announce the launch of several series of live online Torah classes! One will be on "Zoology and Torah," the other will be on "Science and Torah." These will be interactive classes running with the latest videoconferencing software. The classes are free; you just need to register. For details, including information on several other fascinating courses that will be of particular interest to readers of this blog, see It's a unique opportunity for in-depth learning on these topics, so register now, and tell your friends!

Wednesday, November 4, 2009

Blue Whale Washes Up in California

This the tragic sight of a member of the largest species ever to have existed - the blue whale - washed ashore after being struck and killed by a passing ship.

Read more here.

Best Wild Animal Picture of 2009

"The Storybook Wolf"

From National Geographic:

This nighttime shot of a wolf leaping into a farm in northern Spain has been named overall winner of the Veolia Environnement Wildlife Photographer of the Year 2009 competition.

The picture, by Spanish photographer Josi Luis Rodrmguez, was selected from more than 43,000 entries. Iberian wolves--a subspecies of the gray wolf--are extremely wary of humans after centuries of persecution. Rodrmguez captured the photograph using motion sensors and an infrared barrier to operate the camera.

"This wolf jumping over the farmer's enclosure with the supposed intent of killing his livestock speaks for itself--thousands of years of history are frozen in this masterfully executed moment," competition judge and nature photographer Jim Brandenburg said in a statement.

(see the runners-up here)

Friday, October 9, 2009

Elephant Birth

Absolutely extraordinary, but not for the squeamish!

Wednesday, September 23, 2009

Perek Shirah: Nature's Song

I am pleased to announce that my book Perek Shirah: Nature's Song has been republished after being out of print for several years. The new edition also has various minor corrections and improvements over the old edition, as well as a redesigned cover. It is available now at bookstores in Israel and the U.S., and should eventually be reaching other countries too. You can learn more about the book and order it online here.

Monday, September 21, 2009

The Shofar and the Dog

Thursday, August 20, 2009

Exotic Shofars

It's shofar season! You can download the essay Exotic Shofars: Halachic Considerations here. If you live in Israel and would like to arrange a presentation on this topic for a shul/yeshivah/etc., in which I bring my full collection of shofars, please write to me at

Thursday, August 6, 2009

The Secret of the Stincus

It’s exciting when a package arrives via FedEx Special Overnight Delivery. It’s even more exciting when the package is marked “LIVE REPTILES – HANDLE WITH CARE.” The three charming specimens inside looked none the worse for wear despite their long voyage. I was pleased to get them, but if I were Rabbi Yom Tov Lipman Heller (1578-1654), I would have been even more thrilled.

Rabbi Heller was presented with a problem. The Torah mandates that for a fish to be considered kosher, it must possess fins and scales. The Talmud states that every fish that possesses scales, also possesses fins. But Rabbi Heller was presented with a specimen of a fish that appeared to contradict this principle:

...When I was Av Beis Din… in Vienna, the scholar Rabbi Aharon the doctor brought me a fish called Stincus Marinus in the local tongue. It is found in the Spanish sea, and it is poisonous, and the pharmacists know techniques for removing the poison, and then they make various remedies from its flesh. …It has scales over all its body, and it does not possess any fin, but rather it has four legs like those of a domesticated or wild animal. (Ma’adanei Yom Tov to Rosh, Chullin 68:5)

The fact that the Stincus marinus had legs and would thus not be zoologically classified as a fish does not automatically help; the Torah does not follow the classification system of modern zoology (and hence bats are listed amongst the non-kosher birds). Still, Rabbi Heller proposed this as a possible solution, suggesting that it is classified as an aquatic animal rather than a fish, and is not part of the Torah’s discussion. He also suggests another possibility, that it is a hybrid creature produced after Talmudic times, and thus not included in the Talmudic principle that every fish with scales also possesses fins. But Pri Chadash considers both of these explanations difficult, and answers instead that the Stincus marinus must have indeed had fins at some stage in its life, and that it is indeed kosher. Rabbi Yonasan Eybeschitz, on the other hand, is not bothered by the Stincus marinus at all; he explains that, like all such principles, the Talmudic principle that every fish with scales also possesses fins is simply a general rule covering the majority, which could easily have exceptions.

As it turns out, there is an even simpler solution to the problem of the Stincus, later clarified by Chassam Sofer. The Stincus marinus, which I am watching in its vivarium as I type these words, is not only not a fish, it is not an aquatic creature at all. Instead, it is a lizard from the skink family, known by the Latin name of Scincus scincus. I was able to confirm this identification from nineteenth century works which refer to this animal by the name Stincus marinus and which say that it has long been known by this name. Furthermore, this lizard perfectly matches the description given by Rabbi Heller in Ma’adanei Yom Tov. The widespread legends of skinks possessing a poisonous bite or sting are baseless, but certain skinks are toxic if ingested. Scincus scincus was widely used in pharmaceutical preparations, and it is also sometimes known as Scincus officinalis (“pharmaceutical skink”).

But why would Rabbi Heller have thought that it was a type of fish? First of all, he clearly did not see a live specimen. And the dead specimen was presented to him under the name Stincus marinus, which means “aquatic skink.” The lizards of the genus Scincus are known in English as “sandfish.” This is because, although they are not aquatic, these skinks “swim” through sand, beneath the surface. On July 17th, the same day that I received my sandfish, the major science news outlets all ran a report about a breakthrough study on sandfish. It had previously been thought that sandfish swim through sand via a swimming stroke resembling the front crawl, pushing the sand behind it with its feet. But Daniel Goldman of Georgia Tech, in a study published in the journal Science, showed that this is only when they first enter the sand. Using high speed X-ray imaging, Goldman discovered that as soon as the sandfish is submerged beneath the sand, it tucks in its legs and swims through the sand by undulating its body, just like a fish. According to Goldman, “the results demonstrate that burrowing and swimming in complex media like sand can have intricacy similar to that of movement in air or water, and that organisms can exploit the solid and fluid-like properties of these media to move effectively within them.”

So the sandfish truly deserves its name, and it is not at all surprising that Rabbi Heller was told that it was an aquatic creature. Indeed, the idea of an aquatic lizard is not at all impossible; the Galapagos Islands are home to the marine iguana. The extraordinary secret of the Stincus is that you don’t have to be a fish in the water in order to swim like one.

(To subscribe to these essays by email, send an email to

Tuesday, August 4, 2009

Frog Techiyas HaMeisim

One of the things I love about the animal kingdom is that after 30 years learning about animals, there are still new things that blow me away!

(Hat tip - BB from Australia.)

August Programs in NY

Shabbos August 8th: Magen David of Deal, NJ

Sunday August 9th: Kew Gardens Hills
7:45 pm (following mincha at 7:30 pm)
One People, Two Religions: Rationalism vs. Mysticism
9 pm (following maariv at 8:45 pm)
Worlds in Collision: The Dynamics of a Ban

Congregation Etz Chaim
147-19 73rd Ave, Kew Gardens Hills, NY 11367
The lectures are for men and women
Entrance Admission: $10 for one lecture, $15 for both
Download a flyer here

Thursday August 13th
Young Israel of Great Neck
Details to be announced

Shabbos August 15th
Young Israel of Great Neck

Friday, July 31, 2009

Los Angeles Zoo Torah Event

Instead of the tour of the LA Zoo, I am pleased to be able to offer the Zoo Torah Experience, a multimedia presentation on Judaism and the animal kingdom. It will be held at Beth Jacob, 9030 W Olympic Blvd, this Sunday morning at 11 am. The entrance donation is $10, and it is aimed at adults and kids aged 8+. See you there!

Tuesday, July 28, 2009

The Torah Tour of the LA Zoo - CANCELLED

Unfortunately the tour of the LA Zoo has been canceled - see the below email. I am trying to arrange a replacement event with a multimedia presentation at a local synagogue. Please write to for more details.

---------- Forwarded message ----------
From: Jason Jacobs
Date: Thu, Jul 30, 2009 at 8:29 AM
Subject: Zoo Tour on Sunday


Thanks for your phone call yesterday, per our phone conversation, we are requesting that you remove the information regarding your L.A. Zoo Tour from your blog and officially cancel the tour.

The Los Angeles Zoo does not allow outside groups to come in and charge our visitors for tours, promotions, services, etc, without being coordinated thru the Zoo's Public Relations and Marketing Division.

Thank you,
Jason Jacobs
Director of Public Relations & Marketing
Los Angeles Zoo

Thursday, July 23, 2009

Beluga Encounter

Here are pictures and a video from my amazing encounter with beluga whales at SeaWorld California.

Tuesday, July 21, 2009

And the answer is...

Beluga whale!

What an amazing experience. Belugas are a beautiful white in color and very gently. About twelve feet in length, they hail from arctic regions. More pictures to come!

Guess the Animal!


Here's a picture that my wife took of me three hours ago. Guess which animal it is (and it's not as obvious as it might appear!)
Posted by Picasa

Thursday, July 16, 2009

Here Be Dragons

I took this photo on Sunday at the Denver Zoo. The reptile pictures is from a family of lizards known as the sailfin dragons, and this species is Gonocephalus grandis, variously known as the Giant Forest Dragon, Great Anglehead Lizard, or the Giant Hump-Headed lizard. Isn't it incredible?!

Monday, July 6, 2009

Bigfoot in the Mir

Mir Yeshivah, Jerusalem, ten years ago. My chavrusa (study-partner) and myself were puzzling over the first Mishnah in chapter four of tractate Shabbos. It states that one may not on Shabbos insulate a cooked food with straw, dung, and suchlike, “because they increase the heat of the food.” My chavrusa and I were trying to understand how that is possible.

“I’ve got it!” I exclaimed. “These things ferment and decompose, producing heat in the process.”

“How did you figure that out?” asked my chavrusa.

“A little bird told me,” I replied.

And the funny thing was that I wasn’t just using a figure of speech. A little bird really had taught me the explanation.

Mallee-fowl are a group of birds found from Malaya to Australia. About the size of a chicken, mallee-fowl are unusual in appearance in that they possess extremely large feet; hence their scientific name megapodes, which is Greek for “big foot.” The extraordinary thing about mallee-fowl, however, is not their feet, but the way in which they incubate their young.

Birds lay eggs, and eggs have to be kept warm. Most birds accomplish this with the most obvious local heat source: that of their own bodies. But mallee-fowl use a different system entirely. During the winter, the male mallee-fowl excavates a hole in the ground. Astonishingly, this hole can measure four feet deep and twelve feet across. It then proceeds to fill this hole with every scrap of vegetation in the area and covers it with a layer of sand.

The moist, warm vegetation begins to decompose. Bacteria eat away at the organic material. As a result of this process, heat is given off, and the incubator begins to warm up.

Now it is ready to receive eggs. The female mallee-fowl arrives, digs a hole in the litter, and lays her eggs. The male mallee-fowl then covers the area with a mound of earth that can measure up to fifteen feet high and thirty feet across. This little bird with big feet can move half a ton of earth in day!

Organic matter produces heat as a by-product of its decomposition. This is why such material may not be used on Shabbos to insulate food. The concern is that if one uses such material for insulation, one may come to use even better heat-emitting material – embers. And if one uses embers, one might come to stir them up, thus transgressing the prohibition against kindling fire and cooking.

Still, we might wonder how much heat decaying leaves can actually produce. Is it really enough to warrant prohibiting it as a safeguard against using embers?

Well, a commonly used example in the Gemara of a food that cooks easily is an egg. And the mallee-fowl’s incubation chamber can, if not correctly administrated, produce so much heat that it will actually cook its eggs rather than hatch them. Astonishingly, the mallee-fowl manages to detect and prevent this from happening.

Mallee-fowl eggs need to be incubated at a steady temperature of 95 degrees Fahrenheit. The mallee-fowl’s beak is extremely accurate at sensing temperatures, and it constantly plunges its beak into the mound to measure the heat. When the mallee-fowl detects that the rotting vegetation is giving off too much heat, it uses its big feet to rapidly kick away the mound, sometimes until the eggs are virtually uncovered. When the temperature has adequately dropped, it covers them up again.

Eventually, the mallee-fowl’s remarkable work pays off and the eggs hatch. A slight disadvantage of the incubation technique is that the emerging chick finds itself buried under several feet of hot sand. It digs its way to the surface, a procedure that can take up to fifteen hours. Soon it is strong enough to run away, and within a few hours it can fly.

I told my chavrusa about the mallee-fowl, and he was quite taken aback (actually, I’m not sure if he really believed me). Personally, I was struck by the novelty of the situation. In the heart of the ultra-Orthodox section of Jerusalem, my chavrusa and I were poring over a two-thousand year old text and were aided by a bird living eight thousand miles away. It gave me fresh insight into one of my favorite verses from the Torah: “He teaches us from the beasts of the earth, and from the birds of the Heavens He makes us wise.”

(This essay was sent to the Zoo Torah mailing list - to sign up, send an email to

Friday, July 3, 2009

July Programs UPDATED

Here is the schedule of Zoo Torah programs this month:

Shabbat July 11th - Lectures at East Denver Orthodox Synagogue
Sunday July 12th - Torah Tour of the Denver Zoo
(write to to sign up)

Shabbat July 24th - Lectures at KINS
Sunday July 25th - Torah Tour of the Lincoln Park Zoo
Special Lecture: The Challenge of Dinosaurs
Click here for details.

Los Angeles
Wednesday July 15th - "One Judaism, Two Religions: Rationalism vs. Mysticism" - 8.15pm at Young Israel of Century City. Admission $10. Books will be available.
Shabbat July 18th - "The Copernican Heresies" - YINBH

Sunday, June 7, 2009

Real Live Cartoon Creature!

(It's a pygmy jerboa.)

Thursday, May 28, 2009

Torah Tour of the Bronx Zoo

The Torah Tour of the Bronx Zoo
with Rabbi Natan Slifkin
Sunday, May 31st, 2009
First tour 10am – 1pm; Second tour 1pm-3.30pm
Price: Adults $20, children $15
(does not include admission)
Registration is required; email
Limited number of spaces available!

Download a PDF flyer for this event by clicking here.

Wednesday, May 20, 2009

Angry Chameleon

(This video serves to accompany the essay on chameleons in the Torah, that was sent to the Zoo Torah mailing list. To subscribe to the list, send an email to

Thursday, May 7, 2009

On Eagle's Wings

The most prominent bird in the Torah is the nesher, the king of birds. Although many assume that this is the eagle, and some of the commentaries have identified it as such, the evidence shows that it is more likely a vulture - specifically, the griffon vulture (see full essay here).

Curiously, the best-known Scriptural description of the nesher is also the most problematic to understand. It occurs in reference to God bringing the Jewish People out of Egypt:

"You have seen what I did to the Egyptians, and how I carried you (va'esa eschem) on the wings of nesharim, and brought you to Myself." (Exodus 19:4)

The conventional translation of va'esa eschem is "I carried you." However, some translate it as "I elevated you." The explanation is that the nesher is the highest-flying bird, and God raised the Jewish People to spiritual heights above anything in the natural world with His miraculous redemption.[1] The highest flying birds are griffon vultures.

But many explain this verse instead to refer to God poetically carrying the Jewish People like a nesher carrying its young on its back. This relates to a description of the vulture later in the Torah:

"As a nesher stirs up its nest, flutters over its young, spreads out its wings, takes them, bears them on its pinions; So did God guide them, and there was no strange god with them." (Deuteronomy 32:11-12)

The description here is of the nesher carrying its young upon its wings while flying. Many have considered this verse to present us with a great difficulty and to require some kind of allegorical or poetic interpretation, since neither vultures or eagles are generally known to carry their young on their wings. Swans sometimes carry their young on their backs while swimming, and jacanas may sometimes carry their young between wing and body while walking. But according to most literature, the only bird of any sort that carries its young during flight is an obscure water bird from Central and Southern America called the sungrebe, which carries its twin young in pouches under both wings.

This remarkable phenomenon was first reported in 1833 by the German ornithologist M.A. Wied. Subsequent generations of ornithologists viewed this report with skepticism or ridicule. However in 1969 Mexican ornithologist Miguel Alvarez del Toro[2] confirmed that soon after hatching, the male sungrebe places each of the two chicks in pouches under his wings and departs. An article by B. Bertrand[3] explains: "M. Alvarez del Toro, who observed a nesting pair in Mexico, discovered that the male has a shallow pocket under each wing into which the two young can fit. The pocket is formed by a pleat of skin, and made more secure by the feathers on the side of the body just below. The heads of the chicks could be seen from below as the bird flew. Alvarez del Toro collected the bird in order to examine it and confirm the unlikely discovery. Subsequently, he found it confirmed also by a report published by Prince Maximilian of Wied 138 years earlier but apparently ignored, forgotten or not believed. This adaptation is unique among birds: in no other species is there any mechanism whereby altricial young can be transported...."

But eagles and vultures, despite being widely studied, are not described as displaying such behavior. It is therefore suggested that the Scriptural account of the nesher carrying its young be interpreted via the principle of "the Torah speaks in the language of man," as used by several recent and modern authorities to explain other phrases in the Torah that are scientifically inaccurate (such as references to the "firmament," to the hare bringing up its cud, and so on).

However, unbeknownst to many, reports do indeed exist of eagles carrying their young on their backs. One ornithologist writes as follows:

"Many ornithologists have thought that the Bible picture of an eagle carrying her young was merely figurative, but in recent years certain reliable observers have actually seen a parent bird let its young rest for a moment on the feathered back - especially when there was no other roosting place in sight. When an eagle nests on the ledge of a sheer-walled canyon, many feet above the earth, with no jutting tree or protruding rock to break the fall, the quick movement of a mother bird to offer her own back to a frightened fledgling may be the only way to let it live to try its wings again." (V.C. Holmgren, Bird Walk Through The Bible [New York: Dover Publications 1988] p. 98)

One report of this behavior is as follows:

"Our guide was one of the small company who have seen the golden eagle teaching the young to fly. He could support the belief that the parent birds, after urging and sometimes shoving the youngster into the air, will swoop underneath and rest the struggler for a moment on their wings and back. ... Our guide, when questioned, said that every phrase of the verse [Deut. xxxii, I I] (which was new to him) was accurate, save the first; he had seen it all except the stirring up of the nest." (W.B. Thomas, Yeoman's England [1934], pp. 135-6)

Another report concerning the golden eagle comes from Arthur Cleveland Bent, one of America's greatest ornithologists, on the authority of Dr. L. Miller:

"The mother started from the nest in the crags and, roughly hand-ling the youngster, she allowed him to drop, I should say, about ninety feet; then she would swoop down under him, wings spread, and he would alight on her back. She would soar to the top of the range with him and repeat the process. Once perhaps she waited fifteen minutes between flights. I should say the farthest she let him fall was a hundred and fifty feet. My father and I watched him, spellbound, for over an hour." (A. C. Bent, Bulletin of the Smithsonian Institution CLXVII [1937], 302) (Note to the reader: I would be indebted to anyone who can obtain a copy of this article for me, or who knows of any other reliable reports of such behavior.)

True, these reports concern eagles, whereas evidence shows the nesher to be the griffon vulture rather than the eagle. However, it is possible that such behavior likewise occurs with griffon vultures, or that nesher is a generic term encompassing both eagles and griffon vultures. Another solution to the entire question is to posit that "the Torah speaks in the language of men," which, according to one school of thought, means that it packages its messages within the scientific worldview of the generation that received the Torah. For more on this approach, see my essay "The Question of the Kidneys' Counsel."

If referring to a griffon vulture, these verses show that the vulture is regarded by the Torah very differently from the way that it is perceived in contemporary culture. While people today view the vulture in a negative light, the Torah presents it as an example of a loving and caring parent. This also relates to the vulture's entire parenting process. Female griffon vultures usually lay one egg, which both parents incubate for an unusually long period of around seven weeks until it hatches. The young are slow to develop and do not leave the nest until three or four months of age. The long devotion of the vulture to its young symbolizes God's deep dedication to the Jewish People.

[1] See HaKesav VeHaKabbalah ad loc.
[2] Alvarez del Toro, M. (1971) "On the Biology of the American Finfoot in Southern Mexico," The Living Bird 10: 79-88.
[3] Bertrand, B. C. R. (1996) Family Heliornithidae (Finfoots) in del Hoyo, J., Elliott, A., & Sargatal, J., eds. Handbook of the Birds of the World. Vol. 3. Lynx Edicions, Barcelona.

Friday, May 1, 2009

The Dignity of Pigs

In light of swine flu being in the news, and the much-reported position of MK Rabbi Yaakov Litzman that the virus should be named Mexian Flu instead, I thought that the following story would be pertinent:

A number of years ago the Moetzes Gedolei HaTorah of America was concerned about new attempts within the State of Israel to divest the State of any Jewish identity. There were some secularists who argued that Israel should not be a “Jewish” state, but a “state of its citizens,” and the United States was seen as a model. They wanted to abolish all laws that enacted public respect for Shabbos, the Festivals, Kashrus, and other “symbols” of our spiritual heritage. One of the new laws that they wanted to enact would have the government encourage the importation of pig meat. This law was opposed by Orthodox and traditional Jews, including most of the Sephardic population. It was also opposed by some secular-oriented Jews who felt that Israel should publicly honor basic Jewish traditions in order that Israeli culture not become a “carbon copy” of American culture.

The Moetzes Gedolei HaTorah decided to issue a public statement expressing its concern about these developments. A text was drafted and circulated among the members for their consideration and comment. As is usually the case when the Moetzes Gedolei HaTorah issues a public statement, each member of the body of Torah sages reviewed the proposed text with a fine-tooth comb, one suggesting the deletion of a sentence here, another suggesting the addition of a paragraph there, yet another suggesting a different way to structure the statement.

Then Rabbi Pam got on the phone: “It’s very good, except for one problem. The sentence about the importation of pigs is written in a way that could be seen as demeaning to the pigs. Vos iz er chazir shuldig az er iz a chazir? Der Eibishter hut em azoi bashafen! (Why should the pig be faulted for being a pig? The Almighty created him that way!)”

Rabbi Pam added: “A statement from the Moetzes Gedolei HaTorah must be extremely careful not to undermine kavod habriyos — the inherent dignity of all God’s creatures. Let’s reword it this way...”

(Rabbi Chaim Dovid Zweibel, Hamodia English Edition, Ellul 5, 5661 /August 24, 2001). Reproduced in David Sears, The Vision of Eden pp. 222-224)

(more posts on pigs to come)

Thursday, April 30, 2009

The Graceful Giraffe

Wednesday, April 22, 2009

Wednesday, April 1, 2009

Feeding Pets on Pesach

Here is the relevant information about feeding pets on Pesach from my book Man and Beast:

Dear Rabbi Slifkin,
I want to ask you a question about my hamster over Passover. I do not know what I am going to do with her over Passover, as I have asked my Rabbi, he suggested that I ask you. He has said that I should give her away to a non-Jewish person that I know, because the food is not acceptable on Passover. What should I do? I don’t want to give her away for Passover, so could I not feed her only vegetables and sunflower seeds (her favorite) and throw away the other food? Even if I did give her away could I go over to the people that would be keeping her and play with my hamster? Please will you tell me the answer, as I am really desperate to know! Thank you very much and have a great Passover!

A person is not only prohibited from eating chametz (unleavened bread) on Passover, but also from owning it or deriving any benefit from it. Thus, one may not own pet food that contains chametz or feed one’s pet with it during Passover. One may not even allow one’s pet to eat chametz that is given to it by a non-Jew.[1] However, a person is permitted to sell his pet to a non-Jew for the duration of Passover. The animal should be housed in the home of the non-Jew.[2]

Jews of Ashkenazi extraction have a strict custom not to eat kitniyos – various legumes – on Passover. However, it is fully permitted to own such foods and to feed them to one’s animals. As long as they are stored away from any human food, kitniyos often make good pet food for Passover.

Many pet-owners are confused as to what to feed their pets on Passover, so we shall provide some practical guidance as to which foods are appropriate. Any change of diet should be done gradually, mixing in the Passover diet with the regular food several days before Passover. It is generally not advisable to give matzah to any animals, not even fish.

Dog and cat foods often contain chametz. However, several brands of food that are certified as being kosher for Passover are widely available. Note that the kashrus organizations that publish lists of products which are suitable for Passover often include a list of commercially available pet foods which are suitable. It is not necessary to buy a new food bowl for Passover, but the bowl should be thoroughly cleaned.

Commercial food mixtures for small animals such as rabbits, hamsters, and so on, contain problematic grains. It is best to feed them fresh vegetables, alfalfa, sunflower seeds, and dry corn. Commercial alfalfa pellets can also be purchased.

Birdseed likewise usually contains problematic grains. It is best to feed them with sprays of millet. Birds of the parrot family should be given sunflower seeds, as well as fruits and vegetables.

Most fish-food contains chametz. A simple solution is freeze-dried brineshrimp, bloodworms or tubifex worms, which are available at all pet stores. If one is going on vacation, note that vacation “blocks” for feeding fish usually contain chametz. However, a healthy aquarium, with a mixture of fish and plants, can sustain itself for the duration of Passover without any food at all.

[1] Shulchan Aruch, Orach Chaim 448:7.
[2] Mishnah Berurah 448:33 and Aruch Hashulchan 448:12-13.

Tuesday, March 31, 2009

Cat Food Alert for Pesach

Forwarded from a yerushalayim veterinarian:
Dr. Pet cat food contains actual chametz and therefore, may not be used for Passover despite the fact the product has a label which reads "no chametz." The rabbinate takes this opportunity to remind the consumer public that when shopping for Passover, it is not enough for a product to state kosher for Passover, but this must be accompanied by documentation from a legitimate supervising agency.

I plan to write a post with details of how to feed your pets on Pesach.

Wednesday, March 25, 2009

New Blog

I have decided to set up a separate blog for discussions regarding Science & Torah, and rationalist Jewish thought in general. It's called Rationalist Judaism; the comments on the latest post are especially interesting. Please bookmark it and spread the word!

Thursday, March 5, 2009

Dinosaur Handprints and Evolution

Dinosaur handprint backs widely held theory
New evidence reinforces the theory that birds are the descendants of dinosaurs. Read more here.
(Hat tip - Rafi G.)

Saturday, February 21, 2009

The Biggest Fish in the World

Yesterday I visited an incredible place - the Georgia Aquarium, biggest aquarium in the world. There were many incredible sights, but the highlight was the whale shark, biggest fish in the world, which outside of Japan and Dubai can only be seen in Georgia. Their largest specimen was only half-grown at 22 feet long, in a six million gallon aquarium. It was truly awesome, and I spontaneously pronounced the berachah of Baruch shekachah lo b'olamo. They also had the world's only captive manta ray, just a baby at 450 pounds - it's expected to reach ten times that weight, with a wingspan of 26 feet!

Friday, February 13, 2009

Washington Heights Lectures

Sunday, February 22nd
Washington Heights Congregation (The Bridge Shul)
815 W. 179th St

7.30 The Challenge of Dinosaurs
8.30 The Dynamics of a Controversy

Admission: $10 (covers both presentations)
Books will be available

Thursday, February 12, 2009

The New York Times on Nishtaneh HaTeva

In the New York Times article to which I linked in the previous post, it says the following:
Researchers have long known that bacteria evolve to evade antibiotics, and that parasites, like those that cause malaria, adapt to drugs used against the disease. More recently, researchers have reported that cod, overfished for decades off New England and the Canadian Maritime Provinces, have begun reproducing at younger ages and smaller sizes. Other scientists have reported similar changes in species as diverse as bighorn sheep, caribou and ginseng plants.

This instantly made me think of the concept of nishtaneh hateva, "nature has changed," an approach that was introduced in the medieval period to account for disparities between the Talmud and the natural world as perceived in that era. This was that the physical nature of the world had changed since the time of the Sages. While this approach has been grossly overextended, its original application is to the case described by the New York Times.
The primary source for this concept stems from a ruling in the Talmud relating to the age at which cattle and donkeys can bear young. Establishing this age is important because a firstborn animal of these species automatically belongs to a Kohen; thus, when purchasing an animal from a non-Jew, one must ascertain if the animal could have given birth already. If not, then when the animal gives birth, the calf must be given to a Kohen. The Talmud rules that if they are three years old, then when they give birth, their first offspring definitely belongs to the Kohen. Tosafos notes that this is contrast to the facts known in his time:
The explanation of this [ruling] is that before they are three years old, they can certainly not have given birth. But this is astonishing – surely we see all the time that two-year-old cows can give birth! One can answer that times have certainly changed from how matters were in earlier generations. (Tosafos to Avodah Zarah 24b s.v. Parah V’chamor)

This is the same as the phenomenon described in the New York Times!

The New York Times on Shiluach HaKein

The New York Times
February 10, 2009
Seeing the Risks of Humanity’s Hand in Species Evolution

According to the sages who issued the Biblical edicts of Deuteronomy, if you come upon a bird’s nest, you may take eggs and nestlings, but you must leave the mother bird behind. “Let the dam go,” the King James version says.

Some consider this advice as odd as many of Deuteronomy’s other injunctions, like its ban on clothing made of blends of linen and wool. It runs counter to the fishing tradition of throwing the small fry back so they can grow up, aiming for the largest males in trophy hunting.

But now some biologists are starting to think Deuteronomy has it right. They see this approach as a remedy for a growing environmental problem — the way human predation is causing target species to evolve to reproduce at younger ages and smaller sizes, to their short-term benefit but to the long-term harm of the species.

(read the rest here)

(Hat tip: Rabbi Steven Miodownik)

Wednesday, February 4, 2009

Lecture Tour Schedule

Here are the details for the public lectures in my forthcoming lecture tour. I still have some gaps in my schedule so please contact me if you want to arrange something.

Wednesday Feb. 11th, 6.30pm:
"How to Avoid Bear Attacks and thereby Save the Jews"
Stern College

Shabbat Feb. 14th:
Young Israel of New Rochelle

Tuesday Feb. 17th, 8.00pm:
"Sacred Monsters"
Ohel David and Shlomo
710 Shore Blvd., Manhattan Beach, Brooklyn

Wednesday Feb. 18th, 7:30pm:
"The Challenge of Dinosaurs"
The Marcus Jewish Community Center of Atlanta
Atlanta, GA
Suggested donation: $18

Shabbat Feb. 21st:
Ahavas Achim, Highland Park NJ

Friday, January 30, 2009

All the Water and Air on Earth

Conceptual computer artwork of the total volume of water on Earth (left) and of air in the Earth's atmosphere (right) shown as spheres (blue and pink), shown on the same scale as the Earth.

Left: All the water in the world including sea water, ice, lakes, rivers, ground water, clouds, etc. This sphere measures 1390 kilometres across and has a volume of 1.4 billion cubic kilometres. This includes all the water in the oceans, seas, ice caps, lakes and rivers as well as ground water, and that in the atmosphere.

Right: All the air in the atmosphere gathered into a ball at sea-level density. This sphere measures 1999 kilometres across and weighs 5140 trillion tonnes. As the atmosphere extends from Earth it becomes less dense. Half of the air lies within the first 5 kilometres of the atmosphere.

The spheres show how finite water and air supplies are.

(from here)

Friday, January 23, 2009

Lecture Tour

I will be visiting the NY region on an extensive lecture tour during February. I still have some openings in my itinerary from Feb. 12-17th, so if you are interested in arranging a lecture for your shul or a presentation for a high-school, please write to me at

Frogs and Crocs

The second plague to befall Egypt was that of tzefardea. It is widely believed that the term tzefardea refers to frogs, but Ibn Ezra notes that there are actually two views on this matter:

"The commentators differed in their understanding of the word tzefarde'im. Many said it referred to a sort of fish found in Egypt, called al-timsah in Arabic, which comes out of the river and seizes human beings. Others say they are the creatures found in most of the rivers and that they make a sound. This explanation, which is well known, seems correct in my view." (Ibn Ezra to Exodus 7:27)

The former explanation is describing a crocodile. It is referred to as a fish, even though it is a reptile, because the Torah concept of fish also includes other aquatic creatures. Support for this identification is advanced from the description of how the frog plague ceased. The Midrash comments on the statement that the tzefarde’im shall remain in the river:

“ 'The tzefarde’im shall retreat from you and your courtiers and your people; they shall remain only in the Nile' (Exodus 8:7) – Rabbi Yitzchak said, There are still deadly beasts in it that come out and kill people every year ... Moshe did not pray that the tzefarde’im be wiped out, only that they not harm Pharaoh, as it says, 'And Moshe cried out to the Lord in the matter of the tzefarde’im which He had inflicted upon Pharaoh'(Exodus 8:8)." (Midrash haGadol[1])

Rabbeinu Bachya elaborates at greater length:

"Moshe’s words in his prayer stayed true for that time and for all generations. In accordance with his words, 'they shall remain only in the Nile,' to this very day the creeping water creature known as the al-timsah remains there. There it lives, and it is said that sometimes it comes out of the Nile where it lives, rising onto the river’s edge and swallowing whatever it finds, even two or three humans at a time. Neither spear nor arrow can overcome its body, unless aimed for its belly. Physicians say it is venomous and that touching its body, even after its death, is harmful to man. It is of the tzefardea type, and from the power of Moshe’s words, this creature remains there... This is also how Rabbeinu Chananel explained it, and regarding this it states, 'Speak of all His wonders' (Psalms 105:2)." (Rabbeinu Bachya, Exodus 10:19)

According to the second identification, preferred by Ibn Ezra, the tzefardea is the commonly found animal that makes a sound – the frog. This is also the explanation preferred by others:

"Some say it looks like a fish, that it is the timsah, which moves its upper jaw, unlike all other lowly creatures, and that it seizes humans and animals passing by the river’s edge. But the correct explanation is that they are the known creatures of rivers and pools." (Sefer haMivchar[2])

We find the following evaluation in Sefer HaToda'ah:

"This type of destructive tzefardea did not exist in the Nile previously. After it was then created, it remains in the Egyptian river forever. It grows in the Nile to a great size, and damages and swallows creatures big and small. It is the tamsah, which is found in the Nile until today, as a memorial to that plague. And there are some of the commentaries who say that the tzefardea referred to here is the small croaking creature, and so it appears from the words of our rabbis in the midrashos." (Sefer HaToda’ah 23)

The midrashim to which he refers describe the frog as a small and weak creature, prey to snakes and aquatic creatures, that is extremely vocal. This description can only match the frog and does not match the crocodile at all.

What of the etymology of the name tzefardea – does that give an indication either way? Some claim it to be a word from an unknown foreign source.[3] It may be a combination of the root tzafar, meaning to chirp (as frogs do), along with the root rada, “muddy marsh,” which is the frog’s favored habitat. But there are those who state that the name tzefardea is a combination of two words, tzipor de’ah, “the bird of knowledge.” Some explain this to refer to the frog, which chirps like a bird and knows when to stop:

"Tzefardea – a creeping creatures that emits cries all night, until morning, and it is tzipor da, 'the knowing bird,' that it knows the time of morning, to cease from its cries." (Chatzi Menasheh[4])

There is another explanation of “the knowing bird” that is more difficult to ascribe to either animal:

Ba-tzefarde’im” – what is this word, tzefarde’a? There was a bird (tzipor) in the Nile that had intelligence (de'a), and when this bird called to them they came, and so they were named after this bird with intelligence: tzefar-de'a. (Midrash Lekach Tov to Exodus 7:28; cf. Yalkut Shimoni 7:182)

Neither frogs nor crocodiles are known to respond to the calls of birds. But there is a suggestion based on this midrash that there are similar reasons for positing that tzefardea refers to the crocodile.[5] There is an account by Herodotus, who visited Egypt in 459 B.C.E., of a small bird picking food from the teeth of a gaping crocodile. It has been suggested that this refers to the Egyptian plover, Pluvianus aegyptius, which has since also earned the name of “crocodile plover.” It is said that while the crocodile rests with its mouth open, these intelligent birds peck at the crocodile’s teeth in search of parasites. The crocodile makes no attempt to eat the bird and is apparently aware of its benefits. The bird is extremely cautious and gives a call when fleeing from danger, thus also warning the crocodile. Perhaps the tzefardea is the crocodile, named after its symbiotic partner, the intelligent bird that cleans it and warns it of danger.

A problem with this charming explanation is that the described phenomenon may not actually be true. The picture above is a digital reconstruction! Whether such a mutual relationship exists is hard to determine; in the zoological literature, few apart from Herodotus are actually recorded as having seen it.[6] One ornithologist claims that “…no reliable observer since then has seen [it] acting as a crocodile toothpick... The myth has been perpetuated in the literature and needs finally to be laid to rest, unless contrary proof can be found.”[7] On the other hand, Israel’s legendary crocodile hunter Ofer Kobi, who spent decades hunting and farming crocodiles in Africa, informed me that he has observed it.[8] If it does exist, it is rare, and seems more likely to be opportunistic rather than symbiotic.

In conclusion, while there are those who have explained the tzefardea of Egypt to refer to the crocodile, its usage in Midrashic sources and its etymology indicate that the frog is the more likely contender, as several of the commentaries conclude. Some suggest that the name tzefardea refers to amphibious herptiles in general, and could thereby include both frogs and crocodiles. This is the explanation given by the Netziv, who states that whereas most of Egypt was plagued only by frogs, Pharaoh and his entourage were attacked by crocodiles.[9]

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[1] Margaliyot edition, pp. 121-122; originally from Mishnat R. Eliezer, p. 354.
[2] Cited in Torah Sheleimah, Shemos 8:16.
[3] Rabbi Yaakov Kamenetsky, Emes LeYaakov, Shemos 7:27.
[4] A collection of manuscripts cited in Torah Sheleimah 7:108. This explanation is also given by Maharil, cited in B’Shmi U’lekavodi Berasiv, tzefardea.
[5] Prof. Daniel Sperber, “The Frog was a Crocodile,” Bar-Ilan University’s Parashat Hashavua Study Center, Parashat VaEra 5759/1999.
[6] “Despite being corroborated by two eminent German ornithologists in the 19th and 20th centuries, this alleged behavior has never been properly authenticated.” Richford, Andrew S., and Christopher J. Mead, “Pratincoles and Coursers,” in Christopher Perrins (Ed.). Firefly Encyclopedia of Birds (Firefly Books 2003) pp. 252–253.
[7] Maclean, G. L., “Family Glareolidae (Coursers and Pratincoles)” in del Hoyo, J., Elliott, A., & Sargatal, J., eds. Handbook of the Birds of the World (Barcelona: Lynx Edicions 1996) vol. 3 pp. 364-383.
[8] Personal conversation at the Crocoloco ranch, September 2008. For further information on Kobi, whose amazing ranches I visited in Kenya and Israel, see
[9] See HaEmek Davar, Shemos 7:28-29 for his ingenious method of deriving this from the verses.

Monday, January 19, 2009

Letter from a Reader

Rabbi Slifkin,

I read your book "Mysterious Creatures" with great intrigue. However, I was greatly disappointed by your conclusion regarding the category you use to introduce the theme of the book. Were you to have taken the time or effort to visit Eretz Yisroel before drawing your conclusions you might have seen for yourself what animals are actually native to the land before spewing your apikorsus. I am attaching a photo of creatures that I have encountered in many parks and open areas around the country, which are arguably certain to be the adnei ha-sadeh described by Chazal (albeit that they may have become domesticated to some degree over the millennia, as I have witnessed adults and children playing with and around these creatures without ever being attacked and apparently with no fear of such an incident).


M. J.
Jerusalem, Israel

Monday, January 12, 2009

Playing Possum

This passage from the Zohar Chadash describes a monkey that plays possum. But there aren't any possums in the Old World. If anyone has any ideas as to which species it is referring to, I would appreciate it!

זהר חדש פרשת תרומה מאמר נפילת אפים
מ"ט. בגין דנפילה דא, דאתמסר בר נש למותא, אצטריך לכוונא רעותיה, ולמעבד נחת רוח לההוא סטרא דשרייא ביה מותא, כמה דעביד קוף בחרבות ובהרים, אחזי גרמיה דמית, ואתחזי דמית קמי חיותא חדא דדחיל מינה. כיון דההיא חיוותא קריב לגביה, וחשיב לקטלא ליה, ולנשכא ליה, חמא ליה נפיל לארעא כמת, וחשיב דאיהו מת, כדין תב לאחורא, ולא מקטרג ליה. ועל דא אסתלקו אלין ב' אתוון, דלא ידע בהו בר קב"ה דלחודוי:

(Thanks to Rav Moshe Tzuriel, shlita, for the reference)

Wednesday, January 7, 2009

Still nothing to do with animals

Today, everyone is talking about the IDF bombing the UN school. The global media is reporting how "Israel claims" that the school was being used for mortar attacks against Israel. This spin makes it sound like this claim is dubious; but in fact, there is incontrovertible video evidence here:

Here is an excellent IDF video that gives an overview of the entire situation:

It's good to see that Israel is finally learning how to fight a PR war, even if the odds are overwhelmingly against us in that department.