The Torah talks about eight creeping animals that convey impurity. Yesterday, we learned that the eggs of these creatures do not convey impurity, as long as they are whole. The shell keeps the impurity safely locked inside.
On today’s daf, the Gemara focuses on one of the eight, called a tzav, which is probably some kind of lizard. (The word does not appear elsewhere in the Hebrew Bible, making the precise definition more difficult to determine.) A beraita informs us that tzav is actually a category of species that includes the arvad.
Marcus Jastrow, who is known for being an excellent talmudic philologist, but not a talmudic zoologist, tells us (not terribly helpfully) that the arvad is another species of lizard. But the discussion on our daf suggests that the rabbis believe it is actually something far more exotic — a novel hybrid species:
Rav Huna bar Torta said: Once I went to the city of Va’ad and I saw that the locals would wrap a snake around a tzav in order to breed the two. After a period of time, an arvad emerged from between them.
And when I came before Rabbi Shimon the Righteous, he said to me, “The Holy One, Blessed be God, said: The residents of Va’ad caused the emergence of a creature that I did not create in My world by cross-breeding a snake and a tzav. I will bring upon them a punishment for the hazard of this uniquely dangerous creature that I did not create in My world.”
Rav Huna’s teacher, Rabbi Shimon the Righteous, reports that God is not pleased with humans cross-breeding species to create new monsters. This is in line with the biblical injunction against the mixing of species (see Leviticus 19:19 and Deuteronomy 22:9–11), which the rabbis deal with in Mishnah Kilayim, a tractate in Seder Zeraim, which has no Gemara. The townspeople of Va’ad face divine punishment for meddling in this way with the natural world.
All the way back on Berakhot 33a, the Gemara similarly testified that the arvad poses a unique danger, this time telling a story with a heroic ending:
There was an incident in one place where an arvad was harming the people. They came and told Rabbi Hanina ben Dosa. He told them: “Show me the hole of the arvad.” They showed him its hole. He placed his heel over the mouth of the hole and the arvad came out and bit him, and it died.
When a deadly arvad threatens a town, the people turn to miracle worker Rabbi Hanina ben Dosa, who baits the creature’s hole with his bare ankle. Upon biting him, the arvad instantly drops dead from tasting his blood — providing the rabbi with a perfect teachable moment:
Rabbi Hanina ben Dosa placed the arvad over his shoulder and brought it to the study hall. He said to those assembled there: “See, my children, it is not the arvad that kills a person, rather transgression kills a person.” At that moment the sages said: “Woe unto the person who was attacked by an arvad and woe unto the arvad that was attacked by Rabbi Hanina ben Dosa.”
Back on our daf, the Gemara is skeptical such a monstrous hybrid as the arvad actually exists. The reasoning is scientific: The rabbis believe that species with different gestation periods, like (apparently) snakes and lizards, cannot be cross-bred. That, says Rav, makes the arvad a miracle within a miracle: It is a miracle that it came into existence, and a miracle that it poses a danger to those who merit punishment.
Read all of Chullin 127 on Sefaria.
This piece originally appeared in a My Jewish Learning Daf Yomi email newsletter sent on September 4, 2026. If you are interested in receiving the newsletter, sign up here.
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