Trivia

During the production, Kirk Douglas was late to the set because he was shooting a commercial endorsement for the Democratic Governor of California, Edmund G. Brown. John Wayne was furious, and was late to work the next day because he was shooting a commercial for the Republican candidate Ronald Reagan.

John Wayne, who had lost his entire left lung and several ribs in major surgery for cancer in 1964, had great difficulty breathing on an airplane while flying to the location for the start of filming and had to use an oxygen mask throughout the journey. Kirk Douglas recalled that he hadn't realized just how fragile Wayne was until this moment.

In the initial release cut of the film, when bare-chested Kirk Douglas walks away after John Wayne leaves his room, Douglas was nude. In other versions, the scene is cut just before Douglas' buttocks are revealed.

Although Keenan Wynn played the crazy old man, he was in fact nine years younger than John Wayne.

The 49-year-old Kirk Douglas performed most of his own stunts.