Most people are familiar with the phrase ‘shell game’ which denotes the shifty moving around of something so that one finds it hard to trace its location. It comes from a trick that is popular with street magicians that have been used for ages to fleece bystanders who try to bet that they know under which cup a ball has been hidden.
Via Mark Frauenfelder, I came across this clip that shows this and other carnival tricks that the customer is guaranteed to lose. The clip opens with the shell game and is explained at the 6:50 mark as a deliberate misdirection
Frauenfelder also links to a slow motion clip to show another way how the trick is done where the sphere has been palmed by the magician who later inserts it under one of the cups not chosen. Unlike the previous explanation, this way you are guaranteed never to win.