Revealing mistake: When Denzil thinks he's going mad seeing Del cross the road, look at the zebra crossing Del is walking on. It's just a bit of carpet rolled down on the ground. (00:49:48)
Hole in One - S4-E3
Revealing mistake: Uncle Albert is seen putting the post back through the letter box. If you watch the scene carefully, the letters appear to pull themselves through, no doubt with a helping hand from the crew.
Hole in One - S4-E3
Revealing mistake: When the post is being posted through the door, you can see the letters appear in the letterbox and then wait a few seconds for Albert to hang his coat up before being pushed through. (00:01:00)
Revealing mistake: When Del sees Denzil skating along and tells him that he's got his money (the butterfly), Denzil gives him a high five and crushes the butterfly. If you look at Del's hand when Denzil goes past him, you can see the butterfly is not crushed at all.
Watching the Girls Go By - S4-E6
Revealing mistake: At the start, Mickey Pearce is playing darts in the pub by Boycie. On the 3rd dart, he actually aims for the floor behind Boycie to make it seem like the dart bounced off the board. (00:01:10)
Chosen answer: An apparent long string of illnesses.