According to Luckhurst, producers weren’t totally sold on Giger and he was only originally just paid for some sketches, but Scott and O’Bannon were excited to work with the artist and brought him on to do a whole lot more. In fact, he worked on the “Alien” sound stages alongside the rest of the production crew for six months and designed both sets and props. One day, he told someone working on the set alongside him “I want bones,” which led to the set being inundated with lots and lots of bones. According to an anonymous source who worked on the film’s set:
“All these trucks pull up one day loaded with bones. They had been to medical supply houses, slaughterhouses, and God knows where else, and the next day the studio was full of bones and skeletons of every possible description […] You’d go into Giger’s studio and you’d see this guy looking like Count Dracula, dressed all in black leather, with his black hair, lily-white skin and blazing eyes […] I don’t think he dares take off these clothes, because if he did you’d see that underneath he’s not human. He’s a character from an H. P. Lovecraft story.”
It’s not totally uncommon for animal bones (and various viscera) to be used in the creation of horror movies, but if the crew member’s recollection is correct and they went to medical supply houses and picked up human bones, that’s on another level entirely. (Then again, they did infamously use real human skeletons for “Poltergeist”!)