Continuity mistake: You see an opening scene where McMurphy is arriving by automobile. When he gets out of the car it is a cloudy dark day. A few seconds later when he is being brought into the hospital with the guards we see them entering the front door together from down the hallway. Now you can see that it is a bright sunny day outside. (00:04:20)
One Flew Over the Cuckoo's Nest (1975)
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Directed by: Milos Forman
Starring: Jack Nicholson, Louise Fletcher, Michael Berryman, Peter Brocco, William Redfield
Genres: Drama
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More mistakes in One Flew Over the Cuckoo's Nest
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.
Trivia: In the scene where Doctor Spivey is interviewing McMurphy, this whole scene is improvised. Spivey (Dr. Dean Brooks) is the ACTUAL doctor of the institute in real life, and was simply told to interview Jack Nicholson (McMurphy) as if he was a real patient. Nicholson had to improvise and get from the beginning of the scene to the end.
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.