flea

fit as a flea in very good health.

☞ The phrase makes reference to a flea's agility.

a flea in your ear a sharp reproof.

☞ Formerly a flea in your ear also meant something that agitates or alarms you, as does the French phrase avoir la puce à l'oreille. Nowadays, it is often found in the phrases give someone a flea in the ear or send someone away with a flea in their ear.