Buster Keaton was crazy. During the filming of Steamboat Bill Jr in 1928, crew members threatened to quit and begged him not to do this scene. The cameraman admitted to looking away while rolling. A two ton prop comes down, brushes his arm and he doesn’t even flinch!
Marlon Brando was in an acting class that was told to act like chickens and that a nuclear bomb was about to fall on them. Most of the class clucked wildly, but Brando sat calmly and pretended to lay an egg. When Stella Adler asked why he said, “I’m a chicken, What do I know about bombs?”