Shell game

The shell game, also called thimblerig, three shells and a pea or the old army game, is a public gambling game in which a player must follow the movement of a small marker hidden under one of several covers, traditionally shells. Played openly it is a test of attention, but in practice the game is almost always run as a confidence trick, in which sleight of hand moves the marker between covers so that the player cannot win. In the slang of swindlers it is a short-con, meaning a fraud that is quick and easy to carry out. The shell game is closely related to the cups and balls conjuring trick, which uses the same hidden-object principle purely as entertainment with no gambling attached.