Amateur Cast: Will Sampson (Chief Bromden) was a park ranger in Oregon near where the movie was shot, and only landed the part because the casting department couldn't find any other Native American actor who fit the character's physical description. Sampson's appearance in this film led him to a modest acting career in TV and B-movies for the rest of his life.
Dr. Spivey was played by Dr. Dean R. Brooks, the real-life superintendent of the Oregon State Hospital who also served as a technical advisor for the film.
Mel Lambert (the harbor master) was a local businessman, rather than an actor. He had a strong relationship with Native Americans throughout the area, and it was he who suggested Will Sampson for the role of Chief Bromden.
Jack Nicholson and director Miloš Forman had a falling-out over McMurphy's motivation during pre-production of the film adaptation, leading to the two men to stop speaking to each other, at least for a while.
Ken Kesey grew more and more dissatisfied with the changes Forman was making to his original story and cut ties to the production near the end.
Creator Breakdown: Emotionally strained by a demanding shooting schedule that kept him 3,000 miles from his girlfriend (and future wife) Rhea Perlman, Danny DeVito developed the coping mechanism of an Imaginary Friend with whom he would have nightly chats. Concerned that his own sanity might be slipping away, DeVito sought the advice of Dr. Brooks, who assured him that there was no reason to worry as long as DeVito could still identify the character as fictional.
Demoted to Extra: One of the reasons why Dale Harding, a major character of the novel, is only given a handful of lines in the film is that William Redfield, the actor playing Harding, was dying of leukemia and was severely ill throughout the filming. Several scenes were written that gave him a more prominent role, but they were never filmed because Redfield barely had the strength and health to perform in the few scenes that he had.
Development Hell: After starring as McMurphy in a 1963 Broadway adaptation of the novel, Kirk Douglas obtained the movie rights and spent a decade trying to obtain funding. By the time that his son, Michael Douglas, was finally able to secure a production deal, Kirk had gotten too old (and/or unbankable) for the role.
Disowned Adaptation: The only time Ken Kesey ever watched any of the movie was when he was channel-surfing one night and randomly came across it. He changed the channel once he realized what it was. He even sued the movie's producers because it wasn't shown from Chief Bromden's perspective (as the novel is).
The script called for McMurphy to leap on a guard and kiss him when first arriving at the hospital. During filming, Miloš Forman decided that the guard's reaction wasn't strong enough, and told Jack Nicholson to jump on the other guard instead. This surprised the actor playing the second guard greatly, and in some versions, he can be seen punching Nicholson.
Forman would roll the cameras when the cast members didn't know it, so he could capture the "real moment".
Billy would definitely be one if Brad Dourif's career playing various creepy, evil characters had already been established.
Those who know Danny DeVito primarily for such sleazy, jerkass roles as Louie DePalma and Frank Reynolds will be surprised by his portrayal of the gentle, ever-smiling Martini.
Role Reprise: A then-little-known Danny DeVito was the only actor to keep his role from the stage version.
Scully Box: When McMurphy first meets the Chief, the Chief must be standing on a lifting box. You can't see his feet in the shot. Jack Nicholson is 5' 10". Will Sampson was 6' 7". In the shot, Nicholson's shoulders appear only to come up to Sampson's elbows. Also, the finished height of most doorways is 6' 8" and Sampson's head appears to extend higher than that in the shot. Even accounting for perspective, he might be on a 5" plus box. Nowhere else in the movie is the height difference so apparent.
The Indian war dance wasn't in the script. It was Jack Nicholson's idea.
According to Josip Elic, Nicholson improvised the scene where he gets on Brancini's shoulders to play basketball. Nicholson told him, "If I fall, I close this picture down for a week." Elic replied, "If I fall, I close this picture down for two weeks."
Kirk Douglas, who'd played McMurphy in the 1963 play and bought the movie rights, planned to star himself, but by the time they got around to making the film he was too old.
Miloš Forman had considered Shelley Duvall for the role of Candy. While screening Thieves Like Us to see if she was right for the role, he became interested in Louise Fletcher, who had a supporting role, and decided to cast her as Nurse Ratched. Duvall later enquired about playing the role of Rose, but was turned down; had she been accepted, this movie would have had all three members of the principal adult cast of The Shining on board, five years before that film's release (the other two being Nicholson and Scatman Crothers, who played Turkle).
Werner Herzog was asked to direct. Hal Ashby was also considered to direct, though he did recommend that Nicholson play McMurphy.
Having played an orderly in the stage production, Michael Douglas originally wanted to play Billy Bibbit in the film. Randy Quaid was considered for the aforementioned role.
