Ten days before the shooting of this film started, Marlon Brando visited Finland. In a press conference, he was asked what his next film would be, he said he did not remember.
Hubert Cornfield, on the Universal DVD commentary, claims that Marlon Brando, in an attempt to humiliate him, tried to seduce Cornfield's wife and, after being turned down, went to tell Cornfield about his efforts. Cornfield told him that he was flattered.
The final shot, with Marlon Brando smiling in a close-up, was particularly difficult to film for director Hubert Cornfield. Brando kept on making silly faces and refused to smile because he was upset that the ending he preferred was not filmed. In the editing room, Cornfield picked out one frame in which Brando smiled before making another face.
At Marlon Brando's insistence, the last scenes of the shooting schedule were directed by Richard Boone, as Brando could no longer tolerate what he considered the incompetence of director Hubert Cornfield.
According to Rita Moreno, she only got her part in this film as ex-boyfriend Marlon Brando used his influence with the producers (her last theatrical feature had been in 1963). Moreno had taken a lengthy hiatus from movies because she didn't want to be typecast as a Latina spitfire like her character in West Side Story (1961), and all that was offered her after her Oscar win was just those parts.