During the fellatio scene the crew walked out of the production refusing to work on the scene. A similar incident happened during the shooting of Basket Case (1982).
On the subway, Brian sees a man carrying a big basket with a lock on it. The character is Duane Bradley w/Belail inside the basket from Frank Henenlotter's previous film, Basket Case (1982).
One of the gurgling sound effects used for Aylmer actually came from star Rick Hearst. Hearst's stomach would make gurgling sounds if the actor drank coffee on an empty stomach. When Frank Henenlotter found this out he had Hearst go into a sound booth and record the noise with a microphone placed against Hearst's stomach.
The theatrical and original home-video releases of his film deleted the most gruesome scenes, such as the "fellatio" gag.