Trivia: The Alien Design for Sil was done by H.R Giger, the same man who designed the Xenomorph in the Alien movies.
Trivia: Creature designer H.R. Giger personally financed the "nightmare train" sequence after the studio refused to fund it due to its high cost and short length. It reportedly cost him nearly $100,000 between paying for the props, the filmstock, the effects and the camera crew.
Trivia: Creature designer H.R. Giger reportedly came up with the way Sil is killed off at the end. In the original script, Sil is merely set on fire with a flamethrower. Giger told the studio the ending was "weak," and suggested that her head should get blown off, and then her body should be burned up, leading to the ending seen in the finished film. Giger also suggested a more elaborate final battle set in a drive-in movie theater with members of the military storming the location, but it went unused for tone and budgetary reasons.