Reference for Chullin 154:8

לא נצרכה אלא שעשאן ציקי קדרה

R'Eleazar said: The rule [in the Mishnah] applies only to the case where there was no foetus within,<span class="x" onmousemove="('comment',' I.e., in that part of the afterbirth which still remained inside the womb there was not found a foetus or any signs of one; this being so, and because of the principle that there can be no afterbirth without a foetus, the foetus must have been in that part of the afterbirth which had emerged so that it was thereby born; hence the afterbirth is forbidden.');">³</span>

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