Reference for Chullin 135:25

וכי תימא

surely we have expressly learnt it [even with regard to beasts], viz. , If part of the afterbirth emerged [before slaughtering the dam] it may not be eaten,<span class="x" onmousemove="('comment',' V. infra 77a. For it may be that the head of the foetus was contained in that part of the afterbirth which emerged, in which case the foetus would be regarded as born and would not be rendered permitted by the subsequent slaughtering of the dam, and the afterbirth which belongs to it would likewise be forbidden.');">¹⁴</span>

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