Revealing mistake: When Jerzei is coming through the door with an axe, you can see the door is paper thin to make it easier to get through. In fact you can see Alexei Sayle being very careful to only chip small bits away because a decent whack with the axe would smash the whole thing down.David Mercier
Revealing mistake: When Vyvyan is trying to show off his finger trick there are two mistakes, 1) the fingers are bent the other way (this shows that the hand is fake), 2) when he cuts off the wrong finger there is blood shooting out but you can see the tube of blood right near his wrist.
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.tw_stuart
Revealing mistake: The guys turn on the TV and discover the channels don't work. When Rik changes the channels, he leans in front of the TV hiding the screen. This is because the 'channel' never changes at all - it's just a picture stuck onto the TV. You can see this when the camera rotates around, just before the screen goes out of view, behind Rik.
Revealing mistake: When Rik is watching 'Nozin' Aroun'' on TV, he dislikes the program and smashed the TV with his foot. You can still briefly see the image of the show on the TV, even though the TV is smashed. This means the effects people didn't take the image off the green screen quick enough. Also, a few seconds later when Rik is talking to Mike, there are spikes of the screen remaining around the edge of the TV. However, they are green - the remains of the green screen.
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.
Revealing mistake: When Rik Mayall is in the middle of the doorway dancing to the Human League record, you can see him abruptly change his dance steps and deliberately move across to his left (our right) to give the two Police officers room to get past him to destroy the record player. He had his back to the front door the whole time and wouldn't have been able to see them come in.UKFilmFan