Chullin 72 - Kosher Slaughter Makes the Meat Ritually Pure
If an animal was in difficult labor and the fetus put forth its foreleg, and one severed it, to ease the mother's pain and then, since it did not help, slaughtered the mother, the remaining flesh of the fetus is ritually pure, since it has been slaughtered together with its mother. The severed limb itself is impure: if the fetus was alive, the limb was severed from a live animal and has the impurity of a dead animal ( nevelah ); and if the fetus was dead, the limb is actual nevelah.
If one first slaughtered its mother and then severed the foreleg, then the flesh of the fetus is impure because it touched the limb - so says Rabbi Meir. However, the Sages say that flesh is impure with a special light impurity decreed by the Sages, which would only make a difference in the case of sacrifices.
All agree that kosher slaughter makes the meat ritually pure. Why? Logically, one could even argue that should be impure, like non-kosher animals. However, since a kosher animal was fit for food when it was young, its slaughter purifies the meat even if it later became a terefah (sick), whereas non-kosher ones were never fit.
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