Reference for Chullin 222:6

דמא דבשרא שכן דמא דכבדא קפי

R'Nahman said in the name of Samuel: The knife with which one slaughtered may not be used for cutting hot food;<span class="x" onmousemove="('comment',' The throat at the time of slaughtering is deemed to be hot so that the knife during the act of cutting will have absorbed blood and will give it out again when used with hot food.');">⁴</span>

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