Blooper

The makeup used for Lorraine's lip disfigurement changes markedly between shots.

During the opening sequence, Mark's camera is somewhat concealed in his coat at chest level or lower. In the subsequent "first person" shots of the prostitute (supposedly showing what's being seen through the camera's viewfinder), it seems to have moved to eye level.

Disappearing seam on prostitute's stockings in opening scenes

The mark that Mark makes on the movie set floor disappears in subsequent shots, then reappears.

When Mark is filming Vivian, he makes a "set" on a red platform. A red trunk appears on the platform between shots.

Amongst the police paperwork inspected by Chief Inspector Gregg are at least two documents pertaining to the film world (and so were probably just on hand when dressing the set): one is from a member of The Blue Peter (1955)'s crew, requesting the return of his insurance card.

When Mark is viewing his own 16 mm version of the police carrying the body of the prostitute from her flat, there are three bystanders shown between the camera and the police and gurney. When the bystanders move, they cast shadows on to the scene, revealing that they are actually standing in front of a motion backdrop. Thus Mark's film is of another film.

The first video of the father's monstrosities features a woman screaming, not a five-year-old girl.

Mark has a strong German accent, despite it being shown that he has lived in England all his life and had English parents.

When Viv arrives at the studio for her late night audition with Mark, there is a POV shot from the gantry as Mark spies on her, overlaid with the sound effect of his camera whirring. In the next shot, Mark's camera can clearly be seen in front of his director's chair as Viv walks onto the set, before Mark descends on the platform.

Mark plays a tape recording of himself at age five, made by his father who had every room in the house wired. Domestic tape recorders were not available until the late 1940s, when Mark would would have been at least 10.

Mark throws a large knife-switch a la Frankenstein or Frankenfurter to turn on the lights and recorders. These are unsafe at mains voltage, and obsolete by the time his father set up the laboratory.

The second victim of Mark is whistling while entering the stage where she is meeting Mark.Her lips movement doesn't match to the sound of the whistle.

As Mark approaches the prostitute on the street in the opening scene of the movie, the wall behind her shows Mark's shadow and a second shadow that appears to be of a crouched person walking with him.