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.
Enforced Method Acting: In order to protect the central mystery of the film, 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 Soze in disguise, spent the entire shoot believing that he was, and only learned the truth the first time he watched the finished film.
Fake Nationality: According to Del Toro, he is playing a "Black Chinese Puerto Rican Jew."
According to Singer's and McQuarrie's DVD commentary, Kobayashi is supposed to be Pakistani with a Japanese name.
Retroactive Recognition: It's hard to tell at first from the camera angle, but if you listen closely to the voice of the doctor who tells Agent Bayer about the Hugarian's condition, you'll realize that it's Clark Gregg, now widely known as Agent Phil Coulson.
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 giddyness carried over into the scene in that they couldn't stop laughing and making jokes. 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.
Benecio Del Toro was allegedly quite flatulent during the filming of that scene, which kept disrupting filming.
Actors were directed to ask Benicio 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 the lit cigarette ended up hitting Stephen Baldwin in the forehead. Both the cigarette's impact and Stephen Baldwin's justifiably angry reaction remain in the final cut of the film.
What Could Have Been: Al Pacino since laments that the role of Kujan is the part he regrets turning down the most.