On today’s daf we learn that there are certain limitations to the rule of the Mishnah. Rabbi Yohanan teaches that if the slaughtered animal was opened and that the fetus had not developed into an animal, rather it has the appearance of a dove, it is forbidden. The Gemara explains that this law is based on the fact that the Torah requires that an animal have split hooves if it is to be eaten (see Devarim 14:6). At the same time, if the fetus has the form of an animal – even without split hooves – Rabbi Shimon bar Yohai teaches that it is deemed kosher based on the fact that the same passage talks about a single hoof. Thus a kalut ben parah – a single-hooved animal born of a cow (or any kosher animal) would be permitted.
Occasionally an animal with split hooves will give birth to a creature that has a birth defect – its hooves are not split. Although such animals do not have the usual indicators of kashrut, nevertheless we can be certain that it is from the family of kosher animals. This would be true even if the newborn animal does not have the appearance of the kosher mother, e.g. it looks like a camel or a donkey; since we know that it was born from a kosher animal it is kosher and can be slaughtered. This is not the case where the fetus does not have the appearance of an animal at all, e.g. when it looks like a bird or a lizard. The Me’iri quotes the Talmud Yerushalmi that derives this from the abovementioned passage that emphasizes that a behemah – cattle – can be eaten when found in cattle, excluding other life forms that are found in cattle.