How's this for a coincidence? Jack Nicholson, Danny DeVito, and Vincent Schiavelli all played mental patients in One Flew Over the Cuckoo's Nest. And all three went on to play insane Batman villains. It makes you wonder if all three villains escaped from the same asylum… (Source.)

Director Milos Forman wanted the mental hospital in this movie to seem real, so he actually used real mental patients as most of the extras. Call it commitment or exploitation—it still makes for a realistic mental ward. (Source.)

When Jack Nicholson agreed to act in this movie, he settled for a percentage of the movie's profits because he thought they wouldn't be able to pay him well for a small indie film. The movie went on to make more than 120 million dollars, so it looks like Nicholson's generosity paid off. (Source.)