Revealing mistake: If you look closely at the scene where McMurphy climbs the fence and falls from the tree, Nicholson's stuntman looks nothing like him.
One Flew Over the Cuckoo's Nest (1975)
1 revealing mistake
Directed by: Milos Forman
Starring: Jack Nicholson, Louise Fletcher, Michael Berryman, Peter Brocco, William Redfield
Genres: Drama
Continuity mistake: When Mc Murphy is strangling the nurse at the end, from above his hat is lying on the floor, but when you see the shot from her angle, he is wearing it again. (01:56:55)
McMurphy: What do you think you are, for Chrissake, crazy or somethin'? Well you're not! You're not! You're no crazier than the average asshole out walkin' around on the streets, and that's it.
Answer: It's better explained in the novel, where the Chief is the narrator. Essentially, he played deaf and dumb, so he'd be left alone by the Nurse and the staff; seeing what they did to the other patients, he figured the less he was noticed, the better. In this way, he is privy to a lot of the seedier goings-on, since they don't think he can hear what they're saying or tell anyone what he's seen.