The Thing of the Missing Ring
Eddie in The Rocky Horror Picture Show usually wears three rings in this continuity error. When he plays the saxophone, though, you can see his hand, which only has two rings on it. The pinky finger ring mysteriously vanishes. When re-shoots are required a long period after the original scene was shot, these types of faults are common.
They frequently enlist the assistance of the wardrobe and make-up departments, as well as the actor, to remember every minute detail.