Chullin, Chapter 4, Mishnah 5. This chapter continues to explore what happens when shechitah and birth intersect, and here the Mishnah takes up a case that arises constantly in practice: an animal is slaughtered, and when it is opened up a fetus is found inside. Does the mother's shechitah permit that fetus, or does the fetus need a shechitah of its own?
The fetus as a limb of the mother
The Mishnah begins: "Hashochet et habehemah umatza bah ben shemonah, chai o meit, o ben tishah meit, kor'o umotzi et damo." One who slaughters an animal and finds inside her an eight-month fetus, whether it is alive or dead, or a nine-month fetus that is dead, may simply tear it open, remove its blood, and eat it.
Such a fetus needs no slaughtering of its own; the shechitah performed on the mother covers it as well. The logic is that a fetus of this sort has no standing as an animal by itself. Halachah relates to it as one of the mother's own organs, on a par with eating her liver or her kidneys. Since it is not a creature unto itself, what was already done to the mother suffices.
One thing does still have to be done. Blood may never be eaten, and just as with any other limb of the animal, the blood must be drained before the meat is eaten. Once the blood is removed, the fetus is permitted.
Rabbi Meir: a full-term fetus discovered alive
The Mishnah continues: "Matza ben tishah chai, ta'un shechitah, vechayav be'oto ve'et beno, divrei Rabbi Meir." If he found inside the slaughtered animal a live, full-term nine-month fetus, that fetus requires its own shechitah.
Why the difference? Because a full-term fetus that is alive is considered its own animal, and not merely part of the mother. Once the mother's shechitah has taken place, this fetus is still living, still moving, and it therefore stands as an independent entity that needs a shechitah of its own.
Rabbi Meir draws out a further implication, concerning oto ve'et beno, the ban on slaughtering a mother animal together with her young within one day. That prohibition is in force here too: since the mother has just been slaughtered, this living full-term fetus may not be slaughtered until the day has passed. Rabbi Meir's position is that already while it lay in the womb it counted as an animal standing on its own.
The view of the Chachamim
The Chachamim rule otherwise: "Vachachamim omrim, shechitat imo metaharto." Even a full-term fetus discovered alive, they hold, is covered by what was done to the mother; her slaughter is what permits it. In their understanding it is not yet a creature in its own right, and so it may be eaten without any slaughtering performed on it.
This, however, is only on the level of Torah law. The Chachamim agree that on a rabbinic level, once the calf gets up and walks around on the ground, it requires its own shechitah before it may be eaten, even though its mother was slaughtered while it was still inside her. The decree was enacted so that people should not come, in time, to eat animals without shechitah at all.
Rabbi Shimon Shezuri
"Rabbi Shimon Shezuri omer, afilu ben shemoneh shanim vechoresh basadeh, shechitat imo metaharto." Rabbi Shimon Shezuri says: picture the fetus that was inside the mother when she was slaughtered being taken out, reaching the age of eight, and now pulling a plow across a field. Even then, the mother's shechitah has already rendered it permitted. It may be put to death by whatever means one wishes and then eaten, years after the fact. In Rabbi Shimon Shezuri's view, the Sages never imposed any requirement of shechitah upon a fetus discovered inside a mother who was properly slaughtered.
The case where all agree
The Mishnah concludes with a situation in which everyone agrees that the fetus requires its own shechitah: "Kera'ah umatza bah ben tishah chai, ta'un shechitah, lefi shelo nishchetah imo." If the mother was not slaughtered but was simply cut open, and inside her was found a live nine-month fetus, that fetus requires shechitah.
The reason is stated in the Mishnah itself: its mother was never slaughtered. There was no shechitah to permit this fetus, and it cannot be treated as part of an animal that underwent a valid shechitah. In such a case all opinions agree that it needs a shechitah of its own.