Midrasz do Kapłańska 11:8

2) Because it is written (Vayikra 11:8) "and their carcass you shall not touch," I might think that Israelites are liable for touching a carcass; it is, therefore, written "of these": there are among these that for which he is liable and that for which he is not liable, (and)

8) (Vayikra 11:8) "Of their flesh you may not eat" — but not of their bones, or sinews, or hooves (i.e., you may eat those). "and their carcass do not touch": I might think that Israelites (as opposed to Cohanim) are exhorted against touching a carcass; it is, therefore, written (Vayikra 21:1): "Speak to the Cohanim, the sons of Aaron, and say to them: For a dead body he (a Cohein) shall not become tamei among his people." Cohanim are not to become tamei to the dead; Israelites are to become tamei to the dead.

9) Now if they are to become tamei to the dead, a severe form of tumah, should they not become tamei to carcass, a lesser form? How, then, am I to understand "and their carcass do not touch"? On a festival (when they are commanded to appear in the azarah).