his, her, etc. ears are flapping
ears are flapping
Said when one suspects that a private conversation is being listened to. If ears are flapping now, we should postpone this discussion until a later time, don't you think?
his, her, etc. ˈears are flapping(British English, informal) a person is trying to listen to somebody else’s conversation: I think you’d better tell me later when we’re alone — ears are flapping here.
Flap here means to move quickly backwards and forwards.