What uneasy feeling does George have about Curley's wife?

George sees Curley's wife as trouble. Lennie thinks she's "purty". George, in turn, warns him to stay away from her.

"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."