While preparing for the climactic demolition of the city walls, a technician mistook a signal from Ken Russell and detonated the explosives before the cameras were rolling. A large chunk of the set had to be rebuilt. However, a documentary on the second disk of the 2012 DVD release of the film contradicts this story. In this documentary, Russell states that it was himself that pressed the button which detonated the explosives without communicating this to the camera team. It is also stated that the scene had to be re-shot a month later as a consequence the cameras missing the destruction of the walls.
A major sequence in which the nuns tear down and ravish a life-sized icon of Christ in an orgiastic frenzy was cut from the film and subsequently vanished. Film critic Mark Kermode discovered the footage many years later. Director Russell was keen to reinstate the scene but found that Warner Brothers were not interested in doing a director's cut. The footage can be seen in a documentary Kermode made about Russell and was subsequently included in an uncut DVD release.
Early in the movie when Urbain Grandier (Oliver Reed) is seen grooming his hair. It is a close-up of him supposedly looking at a mirror in the upper left hand corner of the screen, behind the viewer. Obviously there is no mirror as he consistently misses combing the more egregiously messed up parts of his hair and instead repeatedly combs the portions that are already groomed. In fact when he is done, his hair is still messed up.