@Mangareader
I'm guessing that hitting someone in the chest causes less pain for the attacker, while still causing significant pain for the opponent. Headbutting another person's head sounds rough for both people.
@Mangareader Pretty sure he hit him in the stomach, right below the ribcage.
@Dreadkiwi He's all bones and zero nerve endings. He should be able to headbutt someone anywhere and it wouldn't hurt a bit. Also, when headbutting someone else's head, you need to use your forehead or something to target a vulnerable spot, like the nose, and not just any part of your opponent's head. That's just asking for you to get hurt as much as the other guy.