Continuity mistake: In series 4 episode 9, "Sitting Targets", Nick is going for a stroll on the roof. At one point he says about leaving the hands free. He then supposedly slips and grabs on with 1 hand. But he used 4 fingers to stop him falling. That is not possible.
One flew out of the Cuckoo's Nest - S3-E13
Continuity mistake: Nick pulls a pint of Tetly and it's still frothing up to a head when he puts it on the bar. Camera cuts and now the pint has settled completely. Something that normally takes a minute or two.
Continuity mistake: When Ben is correcting his cards, his hands constantly move.
While You Weren't Sleeping - S5-E9
Continuity mistake: In this episode Ben's bedroom window is to open towards some grassland with no houses opposite. However, in Season 2, Episode 4, Ben is by a neighbour across the street.
Continuity mistake: In one shot, Ben's arms go from beside him, but when the shot changes after Susan has got up off the floor, one of his arms is pointing towards the kitchen and he is clicking his fingers. (00:01:25)
Answer: Easy. He could have got the guitar at any point in his life. As for keeping it in the attic? You're not going to throw out a £1000 guitar any time soon.
Ssiscool ★