David Fincher had to change one aspect of Se7en due to an injury sustained by Brad Pitt during filming. Three years after his feature directorial debut with Alien 3, Fincher moved away from blockbusters for his second movie. His mystery crime film Se7en starred Brad Pitt as Mills, a hotshot detective, and Morgan Freeman as Somerset, a detective who was nearing retirement. The film was praised by critics and wound up grossing more than $300 million worldwide.
Se7en follows Mills and Somerset as they investigate a murder that leads them to discover a serial killer. The movie follows the two detectives as they search for the murderer, who is responsible for the elaborate crimes based around the seven deadly sins. The chase to find the killer, John Doe (Kevin Spacey), takes them throughout Los Angeles as they investigate the various crime scenes and search for John. And even though the movie is primarily a mystery drama, one of the action sequences resulted in a change for Mills' character.
At one point during Se7en, Mills chases John through buildings and the rainy streets of LA, and he falls off a fire escape and hits the ground. From that point on in the movie, Mills has an injured arm with a cast and at first a sling. However, the severity of this injury wasn't part of the original plan for Se7en. When Pitt was filming the chase scene, his arm went through the windshield of a car and he severely injured himself. After Pitt had surgery on his arm, Fincher was forced to rework Se7en and make the injury part of Mills' character.
It might sound easy enough to make Mills' injury work with Se7en, but that wasn't entirely the case. The primary reason the movie moved forward with the added injury was to avoid shutting down production while Pitt recovered. But this added some complications to the rest of the production. Like most movies, Se7en was not shot completely in sequential order. This meant that scenes from the movie that come before Mills' injury had yet to be filmed due to the shooting schedule. So, in addition to keeping Mills in a cast for the rest of the movie, Fincher also had to hide Mills' injured arm when shooting scenes that would take place before.
In the end, Fincher still managed to make these adjustments and complete Se7en without too much difficulty, while Pitt's name was added to a long list of actors who have injured themselves on set. Tom Cruise famously broke his ankle filming Mission: Impossible - Fallout, while Viggo Mortensen broke his toes with an impromptu helmet kick during The Lord of the Rings. For Pitt, the injury that Mills then has throughout the rest of the film serves as a subtle reminder of what the pursuit of John Doe has cost him, but Se7en ends with a much more devastating reveal that Mills and audiences will never forget.