Reference for Chullin 258:8

מאי טעמא דרבי יהודה

refers to the middle clause [which reads]: IF THE ANIMAL WAS SLAUGHTERED THEY HAVE, BY THE BLOOD [OF THE SLAUGHTERING], BECOME SUSCEPTIBLE TO UNCLEANNESS: SO R'MEIR'R'SIMEON SAYS, THEY HAVE NOT BECOME SUSCEPTIBLE TO UNCLEANNESS.

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