Wentworth Miller jokingly admits he was nervous about his character Chris Redfield being similar to his Prison Break (2005) character Michael Scoffield: in both cases, he is in a prison and his first lines are "I know a way out of here".
The original plan was to have some brief flashback sequences which would elaborate on the back-story of Chris and Claire Redfield and reveal the ongoing search of the two siblings to find one another (well established stories from the video games). The idea was scrapped.
The back-story reveals that the trip of Claire and K-Mart from Nevada to Alaska took a lot longer than they had anticipated. When Alice finds the abandoned chopper and reads the diary, there are notes written by K-Mart describing their course. They made many stops for refueling and new supplies and they eventually arrived at Alaska a few days before Alice.
This marks the fourth time Paul W.S. Anderson has written the script for a Resident Evil movie. He has written all of them since the first one. This also marks the second time Anderson has directed a Resident Evil movie, something no other director has done.
After seeing footage of James Cameron's Avatar (2009), Paul W.S. Anderson was sold on the idea of making the film in 3D. He and his crew spent two weeks in pre-production learning how to properly use the 3D camera system.
The opening scene in the movie is quite symbolic - all people are carrying umbrellas in the rain except the zombie girl. "Umbrella" is also the name of the corporation who is responsible for the creation and spread of the T-Virus, on which the main plot of the Resident Evil series is based.
The sequence in Tokyo after the helicopter crash was extended. According to the script, Alice would search through the debris and would discover the body of Albert Wesker. She would shoot him repeatedly to ensure he died. After Alice left, Wesker's body would begin to regenerate and even start forming the majini mouth.
The trivia items below may give away important plot points.
The superspeed that Albert Wesker manifests as well as his grudge against Chris and Claire Redfield are elements from the video games. His climactic fight with the Redfield siblings is an almost shot-by-shot reenactment of a scene directly from the game.
The intention of writer/director Paul W.S. Anderson was that this would be the first film in the series to have an optimistic ending. The producers, however, wanted an intense cliffhanger as the ending. The director added the massive attack, leaving the film open ended.
Despite prominent billing for actress Spencer Locke, her screen time is very limited since she appears briefly at the end. Additionally, the character of K-Mart does not utter a single line of dialogue during the entire film (excluding archive footage from Resident Evil: Extinction (2007)).
First film where Chris and Jill are both present. However Chris and Jill never meet or share any scenes in the film, unlike the Resident Evil games where the two are very close. In fact the couple have worked together in Resident Evil (1996), Resident Evil: Revelations (2012) and Resident Evil 5 (2009).
Chris and Claire confronting Wesker is slightly reminiscence of Code Veronica. Coincidently Wesker first shows his superhuman powers in Code Veronica to Chris and Claire same as in this film Wesker first uses his powers on Chris and Claire in the films.