Revealing mistake: When Alfred is at the station, you can see that the flames are superimposed.
Revealing mistake: At the very start of the episode, there is some rice with a mouse in. You can tell by the way it moves that it's a machine making it move.
Deliberate mistake: In the shot where we see the cars in front of Victor's (shortly after Victor gets out of the car and gets back in when the traffic starts moving) you can see that after the white car on the right that there are no more cars even though the episode takes place in a traffic queue! If you listen to the commentary on the DVD, writer David Renwick points out the mistake and informs us that they had a limited number of cars for the shot. (00:11:25)
Chosen answer: The episode is 'The Pit and the Pendulum' The first episode of series 4.
James Ransford ★