How does Curley’s wife find out what happened to Curley’s hand?

In Chapter Four, Curley's wife tells the men that she knows he was beaten in a fight - that his injured hand did not result from a machine accident. Lennie eagerly tells her "about the rabbits" and she dismisses their plan as a pipe-dream. As he talks, though, she notices the bruises on his face and deduces his role in Curley's injury. She flirtatiously congratulates Lennie on bringing Curley down a notch and Lennie grows increasingly enamored with her beauty.