What is the legality of cannibalism in the U.S?

I know eating a dead(or living) body is illegal, because eating someone when they're alive is ault and eating them after they die is distubing the deceased. But what if someone signs a weaver? what if someone is willingly eaten, say for ritual beliefs or someything? or what if they just say yeah it's okay if you eat me after I die or something. I know this is weird .XD