Trivia: Cesar Romero refused to shave his moustache for the role of Joker, so it's still visible under his makeup.
Trivia: When Harper strikes Puddler in the head with a rasp, Puddler yells the Wilhelm scream.
Trivia: Audrey Hepburn's movie wardrobe was designed by the famous fashion designer, Givenchy. During the film, Peter O'Toole jokingly comments to Hepburn that the cleaning woman disguise she is to wear for the heist will, "give Givenchy a night off."