This would be a feature that would be implemented at a later point, I can imagine. I like the idea. It doesn't really come with that much value to gameplay, though, so I'd say add it when the game is more fleshed out and separating extremities is in the game. Also, I don't think NPCs would be able to tell if it's the head of a Zombie or a "normal" dead person in 90% of the cases?! I'd like to have it. Even if only for...decorative reasons...