Acting in the Dark: In order to protect the central mystery of the film, Bryan Singer kept some of the actors from knowing more about the story than their characters would be aware of — and in some cases actively misled them so they would give performances hinting at red herring solutions. Gabriel Byrne, whose character is suspected of being Keyser Söze in disguise, spent the entire shoot believing that he was, and only learned the truth the first time he watched the finished film.
Actor Allusion: When Sgt. Jeff Rabin (Dan Hedaya) first refers to Verbal Kint to Dave Kujan, he says, "This guy must be protected on high by The Prince of Darkness." In a segment of an episode of 1980s The Twilight Zone, "Dealer's Choice," a group of friends are playing cards and Hedaya's character is revealed to be the Devil.
Award Category Fraud: Kevin Spacey won the Academy Award for Best Supporting Actor category, despite having more than half the lines in the film. One would expect such a performance to be given the main Best Actor category instead. (This may have been done for tactical reasons, as Spacey was not a particularly well known actor at the time, mostly known from Se7en and with this being his Star-Making Role, and the film's promoters may not have wanted him to go against better known stars such as Nicolas Cage, who won the Best Actor award that year; also, Verbal as a supporting character could hide the twist regarding who he is).
DVD Commentary: The commentary is played straight until the final scenes, when director Singer and screenwriter McQuarrie suddenly engage in a heated argument. Portions of the argument fade in and out of the commentary track much like the dialogue of the film's climax. The filmmakers each land a parting insult before the track ends.
Enforced Method Acting: McManus getting a lit cigarette thrown into his eye was an accident. Stephen Baldwin doubling over and swearing, as well as Benicio del Toro's look of panicked alertness, were both actors' genuine reactions.
In the "making of" documentary, both Stephen Baldwin and Kevin Pollak acknowledge that their long-standing feud with each other began on the set of this film. Though neither actor directly states what caused their animosity towards each other, Pollak does mention that Baldwin, in an attempt to stay in character as MacManus, would go around acting tough and sometimes bully the other actors. Baldwin does admit that he was bullying towards Pollak on film (their numerous "stand off" confrontations with each other on screen).
After Kevin Spacey's career was torpedoed in 2017, Gabriel Byrne stated that he very much acted like a sexual predator on set, making the other actors so uncomfortable that filming was completely halted for a while.
Orphaned Reference: In the original script, the opening scene was longer, featuring a subplot of Keaton planting a bomb on the ship. It was shot but later left on the cutting floor. Part of it remained with Keaton asking Keyzer, "What time is it?" Because of the last minute change, all shots of the exploding ship were shot in Bryan Singer's backyard.
The famous line-up scene was originally scripted as serious. The day prior to filming the scene was a long, tense day of filming in a prison. Singer decided to take the cast to lunch the next day, the day of the line-up scene, to lighten the mood. The lunch turned into a "lovefest" according to Bryan Singer, with all the actors becoming giddy. The giddiness carried over into the scene when Benicio del Toro's flatulence provoked endless chuckling. Singer was originally frustrated, but then liked the takes so much and the idea that it shows them bonding in-story, he threw the funniest ones into the film.
Actors were directed to ask Del Toro to repeat himself if his line readings were ever unintelligible. At least two of these ad-libs were included in the final cut.
Hockney: ...What'd he say??
When Redfoot (Peter Greene) flicks his cigarette at McManus (Stephen Baldwin), the actor was aiming at chest level, but in one take the lit cigarette ended up hitting Baldwin in the eye. This take, featuring the Enforced Method Acting of the cast's genuine reaction, was used in the final cut.
Uncredited Role: Peter Greene, the actor who played Redfoot. This may be because the end shows that the character may well have never existed in universe.
Fenster was originally envisioned as an older, seasoned criminal, with Harry Dean Stanton in mind for the part.
Chris Cornellwas also offered a part, and rejected because he felt "I'm too boyish-looking to butt heads with all these criminal murderer people." Once Cornell watched the movie, he felt some regrets.
In the original script, the opening scene was longer, featuring a subplot of Keaton planting a bomb on the ship. It was shot but later left on the cutting floor. Part of it remained with Keaton asking Keyzer, "What time is it?"
Michael Biehn was the first choice for McManus and was approached about taking the role, but he had to turn down the part because of his previous commitment to filming Jade which also had Chazz Palminteri.
Write What You Know: Christopher McQuarrie had previously worked for a detective agency, and this influenced the depiction of criminals and law enforcement officials in the script.