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.
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.
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.