Lenny Montana (Luca Brasi) was so nervous about working with Marlon Brando that in the first take of their scene together, he flubbed some lines. Director Francis Ford Coppola liked the genuine nervousness and used it in the final cut. The scenes of Luca practicing his speech were added later.
During an early shot of the scene where Vito Corleone returns home and his people carry him up the stairs, Marlon Brando put weights under his body on the bed as a prank, to make it harder to lift him.
Francis Ford Coppola held improvisational rehearsal sessions that simply consisted of the main cast sitting down in character for a family meal. The actors and actresses couldn't break character, which Coppola saw as a way for the cast to organically establish the family roles seen in the final film.
Marlon Brando wanted to make Don Corleone "look like a bulldog," so he stuffed his cheeks with cotton wool for the audition. For the actual filming, he wore a mouthpiece made by a dentist. This appliance is on display in the American Museum of the Academy Museum of Motion Pictures in Los Angeles in a special Godfather exhibition
Cinematographer Gordon Willis earned himself the nickname "The Prince of Darkness," since his sets were so underlit. "Paramount Pictures" executives initially thought that the footage was too dark, until persuaded otherwise by Willis and Francis Ford Coppola that it was to emphasize the shadiness of the Corleone family's dealings.
Gray Frederickson: The film's associate producer as the cowboy in the studio when Tom Hagen encounters Studio Head Woltz for the first time.