Visible crew/equipment: When the song "Ace of Spades" is playing, we see the camera pan up to the singer. You see the studio lights reflected in his sunglasses, as well as part of the camera.
Revealing mistake: When Neil starts to sneeze, he carefully puts his hands close to his nose to give the impression that the green jet is coming from his nose. However, in one shot, just before the guys bag him we see the jet appearing from his hand while his hand is several centimetres from his nose.
Factual error: During "Jester Balowski's Medieval Torture Hour," Balowski grabs the guys arm and bends it the way arms are supposed to bend, yet you hear a breaking noise.
Revealing mistake: When Rik jumps in his bed with the magazine and the circular saw comes out, watch closely and you can see the bed and sheets are already in two halves.
Other mistake: Just as Brian Damage says, "Oh, weren't ya?" to Neil, you can see the shadow of Neil's mother on the front door, awaiting her cue to come in.
Revealing mistake: After Mike burns the stumps (aka Rik), the special patch that was set on fire on the back of Rik's overalls is visible.
Revealing mistake: When the vampire is shaving himself in the toilet, the reflection in the mirror of his shaving cream, clothes and gloves is almost, but not quite, identical to his movements. The empty suit in the mirror and the visible part in front of it were shot separately by copying the other part's movements as closely as possible, as the surviving raw footage can prove. It's hard to see, but there is a small difference between the motion of the hands.
Answer: Madness.
jle