- Ability over Appearance: Sister Sara was supposed to be Mexican but Shirley MacLaine was cast instead. Although they were initially unconvinced with her pale complexion, Clint Eastwood believed that the studio was keen on MacLaine as they had high hopes for her film Sweet Charity, in which she played a taxi dancer. Note that this relies upon the stereotype of Latinos, as there are indeed those with pale looks too.
- Completely Different Title: The Finnish title of the film is "Kourallinen dynamiittia", which translates into English as "Fistful of Dynamite".
- Creator Backlash: Budd Boetticher expressed disgust with Shirley MacLaine's bawdy character obviously not looking like a nun as opposed to his idea of a genteel lady whose final revelation would have been more of a surprise to the audience. He asked Don Siegel how he could make an awful film like that with Siegel replying that it was a great feeling to wake up in the morning and know there was a check in the mail, while Boetticher replied it was a better feeling to wake up in the morning and be able to look at yourself in the mirror.
- Hostility on the Set: Don Siegel and Clint Eastwood felt intimidated by Shirley MacLaine onset. Siegel described her as, "It's hard to feel any great warmth to her. She's too unfeminine and has too much balls. She's very, very hard."
- Romance on the Set: New York Magazine critic Gael Greene had a tryst with Clint Eastwood on the set of this movie when she was sent to interview him.
- What Could Have Been:
- Budd Boetticher, who wrote the original script, had planned the film for Robert Mitchum and Deborah Kerr. Lee Marvin was also considered. Kerr's character was a member of the Mexican aristocracy escaping the vengeance of the Mexican Revolution, with Mitchum's cowboy protecting her as he led her to safety to the United States.
- Elizabeth Taylor was the one who brought the script to Clint Eastwood while he was filming Where Eagles Dare with Richard Burton. She was supposed to play Sara, but she had to turn down the role because she wanted to shoot in Spain where Burton was making his latest film.
Trivia / Two Mules for Sister Sara