Reference for Chullin 57:2

ואי אמרת מחצה על מחצה כרוב איטרפא לה

Now if you say that an exact half is equivalent to the greater portion then here the animal is already trefah!<span class="x" onmousemove="('comment',' For it is assumed for the present that an animal which requires the cutting of both organs was being slaughtered, and the pause, occurring as it does after the greater portion of the windpipe has been cut (for that is the equivalent of an exact half according to Rab) , renders it trefah, and no subsequent slaughtering could render it valid.');">¹</span>

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