I could not resist this one: I saw the explanation of the expression ’slapstick’ (as in ‘slapstick comedy’ or ‘slapstick humour’) on a British TV doco on Regency English towns. The Cheltenham Theatre in this era was known for its pantomime productions, in particular those featuring the character Harlequin who originated in Italian comedy theatre. He is recognisable in his diamond chequered costume and magic sword, which he used to create new scenes, conjure a particular atmosphere on stage, or perform tricks.
In the documentary, the theatre historian showed the way the ‘magic sword’ was often made from two long pieces of wood, joined together at one end but loose on the other. When slapped against a leg, the wood made a sharp slapping sound, loud enough to be heard by audience members, and was the signal for the lights to dim, or a new prop or action to appear – hence the ‘magic’, but also how we get the term ‘slapstick’.