The scene where Billy sees Jenny's body distort in the shower was added during the production because director Brian Yuzna felt another shocking scene was needed earlier in the film.
While shooting the infamous "shunting" scenes, Brian Yuzna would put a sign on the sound stage door that read "Abandon all hope ye who enter here".
Brian Yuzna claims he back-engineered the film's plot points based on special effects ideas or gimmicks, stating he was more interested in the surrealism of the story than the logic.
Brian Yuzna cited La escalera de caracol (1946) and El bebé de Rosemary (1968) as the film's biggest influences, particularly in terms of paranoia as a major element.