Reference for Chullin 257:36

ר"ש מטהר:

But whichever view you take [it is difficult]: If at death the limb is considered as already fallen off then it should be unclean as a limb severed from a living animal, and if at death it is not considered as already fallen off then it should be unclean as a limb severed from a carcass! - R'Simeon refers to the first clause [which reads]: LIMBS OR PIECES OF FLESH WHICH HANG LOOSE FROM THE [LIVING] ANIMAL ARE UNCLEAN IN RESPECT OF FOOD UNCLEANNESS WHILST THEY ARE IN THEIR PLACE, AND REQUIRE TO BE RENDERED SUSCEPTIBLE TO UNCLEANNESS.

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