Reference for Chullin 221:1

ומשום שמנוניתא משום דמא מאי

and the point is about the fat;<span class="x" onmousemove="('comment',' So that the liver of a trefah animal, when cooked with other pieces of flesh, will render those pieces forbidden not because of the blood, but because of the fat of the liver which has been absorbed by those pieces. On the other hand, if the liver of a permitted animal was cooked in the same pot with trefah meat, it would not be rendered forbidden, because whilst it is discharging blood it would not be able to absorb anything.');">¹</span>

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