Reference for Chullin 40:14
כל הכשר בשחיטה כנגדו בעורף כשר במליקה
R'Hisda said: We have also learnt the same: If one nipped off [the head of a consecrated bird] with a knife, the carcass, whilst in the gullet, renders clothes unclean.<span class="x" onmousemove="('comment',' I.e., whilst a person is eating an olive's bulk of it, even if he did not touch it, as when it was thrust into his mouth, he becomes unclean and so do also the clothes that he is wearing at the time. This unusual and unique form of conveying uncleanness is found only in connection with the carcass of a clean bird, and is derived by Rabbinic interpretation from Lev. XVII, 15 and XXII, 8. The other modes of conveying uncleanness, e.g., by contact or by carrying, do not apply to the carcass of a bird.');"><sup>8</sup></span>