Reference for Chullin 252:37

וכמה נקיבתה כחוט השערה שאפשר ליגע כחוט השערה:

shall be unclean,<span class="x" onmousemove="('comment',' Lev. XI, 31: These are the unclean amongst all the creeping things: whosoever doth touch them, when they are dead, shall be unclean until the even.');">¹⁷</span>

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