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.
Mike: Where's Vyvyan?
Rik: Well, he said he was going inside to water his plant. Strange that such a ruthless and sadistic maniac as Vyvyan should care for a begonia. Must have had it two years now.
Mike: And it was dead when he got it.
Rik: Yes... Still, give him his credit - he's watered it every day!
Mike: Only because he can't be bothered to go upstairs to the lavatory.