How does Crooks scare Lennie?

Crooks presents Lennie with numerous scenarios in which George won't come back to the ranch, scenarios in which he leaves. The threats Crooks poses cover everything from George's leaving voluntarily to dying in an accident.... but it doesn't stop there. Crooks so enjoys Lennie's discomfiture that he even goes so far as to tell Lennie what will happen if George does disappear.

Crooks bored in on him. "Want me ta tell ya what'll happen? They'll take ya to the booby hatch. They'll tie ya up with a collar, like a dog."

Suddenly Lennie's eyes centered and grew quiet, and mad. He stood up and walked dangerously toward Crooks. "Who hurt George?" he demanded.

Lennie's reaction is anger, but that same reaction is centered around fear. He's frightened.