The hero and heroine are at a Mardigras celebration with ten other people (12 in all). There is a Mardigras cake cut into twelve slices with a token, and the winner of the token gets to be king/queen of the event. Naturally, we want the hero to get the token.
How might this be effected? One way is that if you keep doing the exercise long enough, the hero will eventually get the token after enough cakes are cut. Another way is that you somehow "mark" the token so that the cake-cutter will know which slice to give to the hero.
What do movie makers usually do under these circumstances?