Reference for Chullin 61:11

מלא צואר וחוץ לצואר כמלא צואר דהוו לה תרי צוארי או דלמא

The question was raised: [Does he mean] the width of a neck and another width of a neck beyond the neck, so that the knife is two necks long, or [does he mean to say] the width of a neck and also a little beyond the neck? - Come and hear: IF, WHILST CUTTING, HE CUT THROUGH TWO NECKS WITH ONE STROKE, THE SLAUGHTERING IS VALID PROVIDED THE KNIFE EXTENDED THE WIDTH OF A NECK.

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