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.
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.