Midrasz do Kapłańska 22:5

4) (Vayikra 22:5) ("Or a man who touches any creeping thing by which he becomes unclean, or a (dead) man by which he becomes unclean, to all his uncleanliness") "who touches (any) creeping thing": This tells me only of a creeping thing (sheretz). Whence is animal carcass (neveilah) to be derived (for inclusion)? From "any sheretz." "by which he becomes unclean": to include (becoming unclean not only by touching the whole object, but even particles of) the size required for uncleanliness. "man": This is a dead body. "has uncleanliness": to include zavim, zavoth, niddah, and yoledeth (a woman after childbirth). This tells me only of their stringent days (i.e., the days of their seeing the discharge). Whence do I derive (the same for) their lenient days? (i.e., the days of their counting)? From "to all of his uncleanliness." "by which he becomes unclean": to include one who cohabits with a niddah. "by which he becomes clean (lit.,) "to it"): to include one who swallows the carcass of a clean bird.