Why does Lennie have to disengage his ear from George? ( Chapter 2 )

Lennie was looking at Curley's wife. George knows that this can only lead to disaster so he twists Lenny's ear.

"Listen to me, you crazy bastard," he said fiercely. "Don't you even take a look at that bitch. I don't care what she says and what she does. I seen 'em poison before, but I never seen no piece of jail bait worse than her. You leave her be."

Lennie tried to disengage his ear. "I never done nothing, George."
"No, you never. But when she was standin' in the doorway showin' her legs, you wasn't lookin' the other way, neither."