The word 'tetragrammatron' has some very interesting origins which render the film either profound or pretentious, depending on your point of view. See http://www.bbc.co.uk/dna/h2g2/A3477909 for a full explanation.

Towards the end of the movie, Preston is in a white suit. This suit was derived from another white suit, worn by Bruce Lee in the film "the Chinese Connection", during the funeral scene.

Director/writer Kurt Wimmer appears three times in the film. The first is in the opening sequence as the silhouetted Cleric performing gunkata movements during Father's voice-over. The second time is as the voice of the Tetragrammaton officer who tells Cleric Preston that they have a warrant for his wife's arrest (in Preston's flashback dream sequence). The third time is as the Resistance member who is shoved up against a column and executed by the police during the warehouse raid (he's the one who holds up his hand in front of his face in a futile attempt to protect himself).

An interesting DVD peculiarity. Switch on the Subtitle feature and then watch the credit roll -- even the background music and the choral singing during the final credits are subtitled. The subtitle "Slow instrumental music plays" is followed by "Indistinct singing".

The scene where Preston clubs a whole bunch of guards to death with his spiked pistol butts took only 30 minutes to shoot.

Originally the emotion suppressing drug everybody takes in the film was supposed to be called 'Librium'. Kurt Wimmer changed it after discovering that there actually is a drug with this name.

The soldiers and resistance fighters, despite this film being set quite some time in the future, are all armed with unmodified modern day weapons. Personally, for those who are interested, I saw G36, G36K, FNC and AK47 rifles, and MP5, MP5K, Skorpion and P90 submachine guns. The clerics, however do have much more futuristic looking weapons. A reference to them being more advanced than ordinary humans, perhaps?

In the scene where Cleric Preston picks up the puppy to keep it from escaping, then hands him back to the Sweeper, the puppy makes several whimpering and yipping sounds. Director Kurt Wimmer had listened to all the "dog" sounds that the sound editor had in his library, but wasn't quite happy with any of them as characterizing the puppy quite right, so they actually hired a voiceover actress whose job it is to characterize dogs to create the puppy's sounds for this scene.

An observation: In 'American Psycho' Bale plays a guy who has absolutely no feelings of any kind but tries to convince those around him that he does. In this film, he plays someone who goes through the entire range of human emotions but pretends he feels nothing. Interesting reversal of character.

The muzzle flash from Cleric Preston's pistols appears in the shape of the Tetragrammaton insignia in several of the gun battles: first, in the nighttime battle over the dog, when Preston first fires his pistol; secondly, several times during the hallway battle near the end of the film (most noticeably just before and after the pistols are reloaded from the wrist-loaders); and finally, when Preston fires the single shot that executes Dupont.

Director Kurt Wimmer designed the Tetragrammaton insignia as four T's, joined at the middle. When the symbol's (unintentional) resemblance to a Nazi swastika was pointed out to him halfway through the film, he was startled and upset, but it was too late to change by then so it was left that way.