Based on the given excerpt, it is clear that the correct answer is: that the men know Benedick has been eavesdropping on their conversation.
In the excerpt, Benedick is hiding and eavesdropping on the conversation between Leonato and Claudio. The fact that Benedick had been hiding and listening suggests that he was intentionally trying to deceive the others by secretly overhearing their conversation. This implies a theme of deception, as Benedick is not being honest about his actions and intentions. The men's awareness of Benedick's eavesdropping further emphasizes this theme, as they are aware that he has been deceiving them by pretending not to be present.