The name John Hobbes is based on two philosophers from the 17th century, Thomas Hobbes and John Locke. Hobbes generally thought that men were evil and needed the constraints of society to make them better. Locke thought that men are thinking, rational creatures capable of peaceful coexistence. These two themes are explored in the film.
In the original screenplay, the role of Gretta Milano (Embeth Davidtz) was originally two characters - Gretta and an elderly sage named Maude who knew much more about Azazel than Gretta. In this version of the story, the cabin in the woods scene was Maude's home.
All of the scenes involving Edgar Reese (Elias Koteas) were shot near the start of principal photography, and director Gregory Hoblit was so impressed with the physicality of actor Koteas' performance that he insisted everyone who subsequently becomes possessed by Azazel must move in a similar manner. Indeed, actors Robert Joy (who plays Charles Olom), James Gandolfini (Lou), Bob Rumnock (who plays the school teacher) and Tara Carnes (who plays the young girl) all studied Koteas' performance before shooting their own possessed scenes.
Although the movie was clearly shot in Philadelphia, the actual location of the story is never clarified (much as was the case with 'Se7en (1995)). The prison in the opening scene is Holmesburg Prison located north east of Philadelphia, opened in 1895 and closed in 1996.
The first scene which writer Nicholas Kazan came up with for the film was the scene where Azazel first passes from person to person (the scene which culminates with the possession of Charles Olom (Robert Joy). Kazan was thinking about how evil can be passed on from one person to another, that it is contagious; if one person is nasty to another person, the second person will be nasty to a third person, the third to a fourth and so on. In thinking about this, he hit on the notion of what that may be like literalized, and he came up with the scene. The rest of the move sprang from that scene.
During preproduction, Elias Koteas traveled to Ohio to meet a man who could speak Syrian-Aramaic, to help him with his dialogue. The man was happy to help, but would not say the swear words in the speech, as he was too religious. As such, the production had to find another Syrian-Aramaic speaker who was willing to speak the profane lines for Koteas.
The first day of shooting was scheduled to be the scene where Hobbes (Denzel Washington) arrives at the cabin for the first time. A huge rainstorm was passing through the area at the time however, so producer Charles Roven decided to send the equipment truck out to the location much earlier than normal, so early that it was still dark. However, due to it being dark, and with such heavy rain, visibility was poor, and on the side road to the cabin (which was the only road to the cabin), the truck hit a tree, completely blocking off the road. By the time the truck was cleared, it was nearly night time again, and no shooting could be done, meaning that one day into production, the film was one day behind schedule. Charles Roven has said that this first day was the worst day of his entire career.
The 'demon vision' footage in the film was shot using a film stock called Ektachrome, which is developed for stills photography. Additionally, the scenes were all shot at 6fps and printed at 24fps, meaning each frame is exposed 4 times. Coupled with camera movements, this technique gives a blurred/streaky quality. A mesmerizer lens was also used, which allows the camera operator to cock the lens several degrees to the left or right.
To shoot the two scenes where Azazel passes through numerous people on a street, the production employed dance choreographer Russell Clark to block out the scenes, which were then shot using primarily dancers.
The scene where the rafter collapses whilst Hobbes (Denzel Washington) is in the basement of the cabin was in neither the script nor the original cut of the film. During test screenings, the scene played out with Hobbes simply looking around, finding the book, and leaving. However, at one particular screening, during that scene, a member of the audience got up to go to the bathroom, and as he left the theatre, the door made a loud bang, causing everyone in the theatre to jump. This prompted the Warner Bros. executives to suggest that perhaps a sudden scare should be shot and inserted into the scene so as to enhance the tension even further.
Despite Warner Bros. titles usually having their pay cable debuts on HBO (since the two companies are owned by Time Warner), this film premiered on Starz due to a previous agreement with the film's producers.
The trailer shows someone possessed by Azazel chasing Gretta Milano (Embeth Davidtz) into a department store through a revolving door. This scene is not in the final film. On the DVD commentary track, director Gregory Hoblit, writer Nicholas Kazan and producer Charles Roven explain that the reason this scene was removed was because the possessed person was trying to stab Gretta, and they realized that having Azazel try to kill her didn't make much sense, and it would be far better to have him try to possess her instead. As such, the scene with Graham Beckel was shot as a replacement.
After shooting the scene where Hobbes (Denzel Washington) tells Sam (Michael J. Pagan) that his father is dead, the production sent a courier to a lab in New York to have the sound and images processed. However, on the way, a journey which involved two taxis and a two hour train ride, the courier lost the sound for the scene. The production took out ads in the newspaper, and ran ads on TV and radio asking anyone who may have found it to return it, even offering a reward. In the end, although many people reported finding lost sound footage, it was never the footage from Fallen. Ultimately, as reshooting was impossible, and as it was felt ADR would not be able to recapture the emotion of the scene, the filmmakers ended up using the sound from the Video Assist machine (the sound was recorded on Hi8 tape). They sent the sound to a sound effects lab, which was able to pull up the sound to the point where it could be used in the film.