Parashas Acharei Mos · Passuk 17:15
Chabad.org — English translation + Rashi
Torah Temima points to Toras Kohanim.
English: Tumah occurs in the “house of the soul” (the throat/swallowing), not while the food is still inside the mouth.
Locus of tumah (beit ha-nefesh)
Garment impurity from eating neveilah begins only upon swallowing, not from food held in the mouth.