"Punch me" joke

Santa and Banta are at work, digging a hole. Banta asks Santa other, "Why is that guy up there sitting under the tree while we do all the work?"
Santa said that he doesn't know, so he goes up and asks him why.
The guy under the tree says, "Because I have intelligence."
Santa says, "What's that?"
So the guy under the tree stands up and says, "Punch me as hard as you can."
Santa winds up and punches him, but the intelligent guy moves away and the digger punches the tree. His hand is now killing him.
Santa says, "Oh, I think I know what it is now."
He goes back down to Banta.
Banta asks, "So why are we doing all the work?"
Santa replies, "Because he has intelligence."
Banta says, "What's that."
Santa looks around for a tree, but doesn't see one, so he puts his hand in front of his face and says, "Punch my hand as hard as you can."