Revealing mistake: When Basil is out of the car and shouting at it after its final breakdown, you can see a crew member reflected in the right hand side of the windscreen giving John Cleese cues. It's not Cleese himself, as the reflection remains after he runs out of shot to get the tree branch, and the reflection doesn't mimic every action performed on screen.
Revealing mistake: In the scene where Polly brings Mr O'Reilly a cup of tea, it is obvious on several occasions that there is nothing at all in the cup. Not only does he hold it in such a way that you can see inside, but when Basil snatches it away nothing spills out.
Add timeDavid Mercier
Revealing mistake: In the part where John Cleese is smacking Manuel's head against the place where the dining room doors are supposed to be, you can see very that Manuel is kicking the wall right when his head is supposed to hit it, creating the sound of his head hitting the wall. Check it out because it's very obvious and hard to miss.