After the prayers don’t work he has a metamorphosis of sorts after watching the half skinned rabbit twitch and squeal and run around. He’s pulling his own flesh off, in a sense, to become less human, to become a deaths-head like he saw on the German officer’s uniform. That’s why the death’s-head moth is brought up – not a butterfly transformation, but a dirty moth with a skull on it.

He’s mute = numb.