Neither Roman spectators calling for the death of a gladiator, nor Roman Emperors authorizing one, ever gave a thumbs down. In fact, the Romans didn’t use a thumbs down sign at all. If death was desired, the thumb was stuck up  — like a drawn sword. For a loser’s life to be spared, the thumb was tucked away inside the closed fist  — as with a sheathed weapon. If further proof were needed, in 1997 a Roman medallion of the second or third century AD was discovered in southern France. It shows two gladiators at the end of a battle and a referee pressing his thumb against a closed fist. The inscription reads: Those standing should be released.

This has been problematic in Iraq, where American soldiers are unsure whether locals are welcoming them or about to blow them up. Desmond Morris traces the positive connotations of the thumbs up in Britain to the Middle Ages, where it was used to close business deals. It found a new lease of life in World War Two when US airforce pilots adopted it as a signal to ground crews before take-⁠off.