We, too, learn in a mishna (Bekhorot 46a) that the fetus of a woman that has the form of an animal cannot survive: In the case of a woman who had previously discharged a fetus with the appearance similar to that of a domesticated animal, an undomesticated animal, or bird before giving birth to any children, and subsequently she gives birth to a son, the son is considered a firstborn with regard to the halakhot of inheritance, but he does not require redemption, as the fetus is considered a full-fledged offspring in that regard. This is the statement of Rabbi Meir. And the Rabbis say: The son is not exempted from the requirement of redemption from a priest unless it follows the birth of a fetus that takes the form of a person; otherwise, it is not considered the offspring that “opens the womb” (Exodus 13:2), and the son requires redemption as a firstborn.

And in the case of a woman who discharges a fetus in the form of a sandal fish, or from whom an afterbirth or a gestational sac in which tissue developed emerged, or who delivered a fetus that emerged in pieces, the son that follows them is considered a firstborn with regard to inheritance but is not a firstborn with regard to redemption from a priest. The Gemara explains the proof: And if it enters your mind that a fetus that has the form of an animal can survive, is the son that follows it a firstborn with regard to inheritance?

Rava said, in rejection of this proof: Actually, it is possible that a fetus shaped like an animal can survive; but it is different there, with regard to inheritance. The son that follows such a fetus has the status of a firstborn, as the verse states with regard to the inheritance of a firstborn: “By giving him a double portion of all that he has; for he is the first fruits of his strength [ono]; the right of the firstborn is his” (Deuteronomy 21:17). It is derived from the verse that the status of a firstborn applies only to a son over whose death a father would mourn. The word ono is interpreted homiletically based on its similarity to the word onen, acute mourner. This offspring that has the form of an animal is therefore excluded, as its father would not mourn over its death.

§ Rav Adda bar Ahava asked Abaye: According to Rabbi Meir, who said that an item that is similar to an animal in the womb of a woman is considered a full-fledged offspring, what is the halakha with regard to a human fetus in the womb of an animal? The Gemara explains: What is the practical difference of this inquiry? The difference is with regard to permitting the fetus in consumption. A full-fledged fetus found inside its slaughtered mother is permitted to be eaten, despite the fact that it was not slaughtered itself.

The Gemara suggests: But one can resolve the dilemma from that statement of Rabbi Yoḥanan, as Rabbi Yoḥanan said: In the case of one who slaughters an animal and finds in it an item that has the form of a pigeon, the pigeon is prohibited for consumption. Evidently, the ritual slaughter of a pregnant animal renders its fetus permitted to be eaten only if the fetus is of the same species as the mother. Accordingly, if the fetus has the form of a human, it is prohibited for consumption.

The Gemara rejects this suggestion: How can these cases be compared? There, with regard to a pigeon fetus, there are no split hooves, and there is not even a hoof at all. Since a pigeon is completely different from the slaughtered animal, the fetus is forbidden. By contrast, here, in the case of a human fetus, although there are no split hooves, there is at least a hoof, i.e., solid feet. Therefore, it is possible that the human fetus is permitted for consumption, and the dilemma remains unresolved.

§ The mishna teaches: And the Rabbis say: Any discharged entity that is not of human form does not render the woman impure. Rav Yirmeya bar Abba says that Rav says: All concede that if a woman discharged an entity whose body is that of a goat and whose face is that of a human, it is considered a human offspring, i.e., even the Rabbis rule that the woman is impure in this case. Likewise, if its body is that of a human and its face is that of a goat, Rabbi Meir concedes that it is nothing, and the woman is pure.

They disagree only in a case where its face is that of a human, but it was created with one human eye and one eye like that of an animal. As Rabbi Meir says that if the offspring has part of the form of a human face, even if one eye is not like that of a human, it is considered a human offspring, and the woman is impure. And the Rabbis say that it must have the entire form of a human face to be considered a human offspring, and otherwise the woman is not impure.

One of the Sages said to Rav Yirmeya bar Abba: But isn’t the opposite taught in a baraita: Rabbi Meir says that a woman who discharged is impure if the fetus has any part of the form of a human face, and the Rabbis say that the woman is impure only if the fetus has a recognizable part of the form of a human face, e.g., half of a human face? According to this baraita, Rabbi Meir does not even require that a significant part of it must look human. In his opinion, even if it has only one human eye or one human cheek and the rest of the face is like that of an animal, the woman is impure. Rav Yirmeya bar Abba said to the Sages: If this baraita is taught, it is taught, and I cannot take issue with it. I have my tradition from Rav, and you should rule in accordance with the baraita that you received.

Rabbi Yirmeya bar Abba says that Rabbi Yoḥanan says: A woman who discharges an entity is impure only if the entire face of the fetus has a human form. This includes its forehead, and the eyebrows, and the eyes, and the cheeks, and its chin. The woman is not impure unless these facial features all as one have the human form. Rava says that Ḥasa says: It is sufficient for the fetus to have the appearance of a human on one side of its face; its forehead, and one eyebrow, and one eye, and one cheek, and its chin are enough. The woman is not impure unless these facial features all as one have the human form.

And Rabbi Yoḥanan and Ḥasa do not disagree about whether the halakha is in accordance with the opinion of Rabbi Meir or that of the Rabbis, as they both accept the opinion of the Rabbis. The difference between them is that this amora, Rabbi Yoḥanan, holds like the one who says that the Rabbis require the entire form of the face to be human, and that amora, Ḥasa, holds like the one who says that the Rabbis require only a recognizable part of the form of a human face.

Ḥasa evidently interprets the version of the Rabbis’ statement that only part of a human face is required as referring to half of a human face. The Gemara raises an objection to this interpretation from a baraita: The miscarriage of a fetus with the form of a human face, which the Rabbis said renders the woman impure, includes even one of the facial features, apart from the ear. Apparently, that is to say that even if the fetus has only one facial feature of a human, this is also sufficient to render the woman impure.

Abaye says: When that baraita is taught, it is taught with regard to the halakha of rendering all of the facial features indispensable for the fetus to be defined as human, except for the ear. And this ruling is in accordance with the one who says that the Rabbis require that the entire form of the face must be human. And if you wish, say that actually this ruling is in accordance with the one who says that the Rabbis require only a recognizable part of the form of a human face. And what is the meaning of the claim that it is sufficient for the fetus to have one facial feature of a human? It means one of each facial feature of which a human has two, i.e., one eye, one eyebrow, and so on.

Rava says: In a case where a fetus was created with one eye or with one thigh, if the eye is located to the side on the middle of the face, or the thigh is located at the side of the hip, where a human eye or thigh is normally located, the fetus is considered human, and its mother is impure. If it appears in the middle of the face or hip, the fetus is not considered human, and its mother is pure.

Rava says: If its esophagus is punctured, although the fetus is considered a tereifa, i.e., one that has a wound that will cause it to die within twelve months, its mother is impure. But if its esophagus is sealed, i.e., it is closed at one end, it does not have the status of a human fetus, and therefore its mother is pure.

§ The Sages taught in a baraita: In the case of a woman who discharges a fetus that has a sealed body, its mother is not impure with the impurity of a woman after childbirth. And what is a sealed body? Rabbi Yehuda HaNasi says: It is a body which is lacking a limb that when removed from a living person would cause him to die.

And how much of the lower part of a person’s body when removed from a living person would cause him to die, because one cannot survive such a wound? Rabbi Zakkai says: