Reference for Chullin 59:37

אמר ליה רבי אבא

[We have learnt,] If two persons held a knife and slaughtered, even if one cut higher up and the other cut lower down [in the neck], the slaughtering is valid.<span class="x" onmousemove="('comment',' V. infra, 30b. It is assumed for the present that there were two knives in use and each person held a knife and cut in a different part of the throat.');">²³</span>

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