Paul W.S. Anderson's initial cut of the film ran 130 minutes, and was so violent that both test audiences and the studio baulked at the finished product. Paramount ordered him to cut the film by 30 minutes and tone down some of the violence. Anderson has said he didn't have enough time for a proper re-edit, and believes he cut out 10 minutes too much. Although it was announced in 2012 that producer Lloyd Levin had found a VHS tape that might contain a full version of the film, Anderson revealed in 2017 that neither he nor Levin had seen it yet, as they have both been too busy to be in the same country with a VHS player. Although he believes that the condition of the copy will be too poor to use, Anderson has stated that he is still excited to see what's on it.
(at around 5 mins) The shot where Sir Sam Neill stares out of a window which then pulls back to reveal he's on the deck of a space station orbiting Earth took the digital special effects house Cinesite 10 weeks to achieve. The shot lasts for 45 seconds and took nearly a third of the film's visual effects budget, because it was filmed using separate scale models of different size that had to match up perfectly. Director Paul W.S. Anderson said that the shot had to be re-done over 20 times before he was satisfied with it, and half-jokingly claimed that the man working on it had to take a year-long sabbatical afterwards to recuperate.
The official name of the Gateway machine in the script was 'the third containment', but it is informally called the "gravity drive" in the film (the room it stands in being the second containment, and the corridor leading to them the first). It was originally described as a smooth and featureless black orb, 10 meters (nearly 33 feet) in diameter, suspended in midair between large, rotating mechanical arms. It also was said to contain a stable black hole within it at all times (which the ship used as a power source), as opposed to briefly creating a temporary one. Paul W.S. Anderson decided to redesign it to involve interlocking rings as a homage to the puzzle box in Le Pacte (1987), which served as an inspiration. The spikes on the curved walls were originally supposed to extend inwards and connect with the machine each time when the drive activated. However, at the end of production, no more time and budget were left to create this as a visual effect.
Although the film met with mostly negative reviews and a disappointing box office result at the time of its release, it amassed a considerable cult following over the years. Director Paul W.S. Anderson said that the movie's cult status was predicted to him years before by Kurt Russell. Anderson screened Event Horizon before they started work on Soldier (1998), and Russell said "Forget about what this movie's doing now. In fifteen years time, this is going to be the movie you're glad you made".
(at around 1h 25 mins) The filming of the fireball inside the gravity drive tunnel caused a real fire that partially destroyed the set. Director Paul W.S. Anderson had a military flamethrower mounted to produce a huge fireball, but due to the force of the jet, it toppled and started to incinerate the wooden ceiling. Anderson ordered the stunt coordinator to switch the machine off, but the controls were on the device itself, so no one could get close to it. It then turned over and started to burn the wooden floor, under which the gas canisters feeding the flame had been placed. The studio was quickly evacuated, but fortunately, the canisters held out until the fire could be put out. A different set had to be built quickly while the old one was being repaired. In the end, the repaired set was only used for an additional day of filming.
Paul W.S. Anderson: (at around 3 mins) During the opening dream sequence, a book floats past the camera, featuring a picture of the director and his name. The director himself jokes about this detail in the DVD commentary saying it's his autobiography, titled "Paul Anderson: A Life". Later, there is a bottle of mineral water floating around of the brand 'Eichinger', an homage to producer Bernd Eichinger with whom Anderson would later make Resident Evil (2002).