any of numerous small, wingless bloodsucking insects of the order Siphonaptera, parasitic upon mammals and birds and noted for their ability to leap.

either of two common fleas of the genus Ctenocephalides, the very small, black C. felis (cat flea) or the similar but larger C. canis (dog flea), both of which infest cats, dogs, and occasionally humans.

any of various small beetles and crustaceans that leap like a flea or swim in a jumpy manner, as the water flea and beach flea. ?

flea in one's ear

a disconcerting rebuke or rebuff

The next time he shows his face around here he'll get a flea in his ear.

a broad hint.