Director David Schmoeller had a lot of trouble directing Klaus Kinski. For example, Kinski refused to listen to basic commands such as "action" and "cut".
When Josef Steiner knocks at Gunther's door, Gunther is reading while eating candy from an open box on the end table. When he lets Steiner in, the box is now closed.
As the heroine is crawling through the ducts, you can tell is she being pulled (or pushed) by some device. She lifts her arms to swat away a rat, but her pace is not slowed.