All of the actors who played patients in “One Flew over the cuckoos nest” (1975) actually lived on the Oregon State Hospital psychiatric ward throughout production. The men personalized their sleeping quarters, spent their days on campus “get[ting] a sense of what it was to be hospitalized” (as actor Vincent Schiavelli put it), and interacting with real psychiatric patients.
Emotionally strained by a demanding shooting schedule that kept him 3000 miles from his future wife, Rhea Perlman, 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.
While Dr. Brooks had no concerns about DeVito, he echoed the rest of the cast and crew’s apprehensions about the psychological state of Sydney Lassick, who played Charlie Cheswick. Lassick exhibited increasingly unpredictable and emotionally erratic behavior during his time in character, a pattern that culminated in a tearful outburst during his observation of the final scene between Nicholson and Sampson. Lassick became so overwhelmed during the scene that he had to be removed from set.
To complete this realistic immersion, Forman led his performers in unscripted group therapy sessions in which he directed the actors to develop their characters’ psychological maladies organically. He would often capture footage of the actors, both in and out of character, without explicitly mentioning that the cameras were rolling. The film’s final cut includes a shot of a visibly irritated Fletcher reacting to a piece of direction fed to her by Forman.