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Dan O'Bannon's idea for the movie came from his experiences on two other projects. He had worked as a writer and special effects supervisor on John Carpenter's Dark Star (1974), a science fiction comedy that started out as a student project, but got turned into a feature film. Halfway during the production of the movie, O'Bannon thought the movie's premise would work much better as a horror movie, so he started work on a script called "Star Beast". Dark Star was a commercial failure, but it was seen by Chilean-French director Alejandro Jodorowsky, who had acquired the rights to Frank Herbert's "Dune". Jodorowsky invited O'Bannon to help him with the book's ambitious adaptation, so O'Bannon sold all of his belongings and moved to Paris to work on the movie. While briefly working on the ill-fated project, he encountered influential artists such as Chris Foss, Ron Cobb, Jean 'Moebius' Giraud (a.k.a. Moebius), H.R. Giger and their unique styles. When Jodorowsky's Dune fell through due to lack of funding, O'Bannon took the creative team and worked on his Star Beast movie (titled Alien at that time), using much of the designs already created for Dune. Sir Ridley Scott, one of the few who had also seen and liked Dark Star, agreed to direct. It has since been said that Alien became the movie that "Jodorowsky's Dune" was supposed to be.
The blue laser lights that were used in the alien ship's egg chamber were borrowed from The Who. The band was testing out the lasers for their stage show in the soundstage next door.
The chestbursting scene was NOT filmed in one take (despite the myth). The scene was filmed twice: on the first take, the chestburster was unable to cut through Kane's shirt, so the crew needed to reset and shoot it again. The failed attempt is visible in the finished film, since director Ridley Scott thought it made it look like the creature was struggling to push its way out, and made the scene more violent (see The Beast Within documentary where this is discussed). According to designer Ron Cobb, the two takes of the scene were shot from multiple angles, and about 40 minutes of footage was available for screening.
Shredded condoms were used to create tendons of the beast's ferocious jaws.
According to Yaphet Kotto, Sir Ridley Scott told him to annoy Sigourney Weaver off-camera, so that there would be genuine tension between their characters. Kotto regretted this, because he really liked Weaver.
To get Jones the cat to react fearfully to the descending Alien, a German Shepherd was placed in front of him with a screen between the two, so the cat wouldn't see it at first. The screen was then suddenly removed to make Jones stop advancing and start hissing.