The Second Time Around - S1-E4
Revealing mistake: When Del, Grandad and Rodney Come Home to the flat after staying with their Aunt, as Del is checking the kitchen you can see Lennard Pearce standing by the door waiting for his cue. (00:26:05)
Revealing mistake: At the end of the episode when Del and Rodney get hit by the car, Del jolts forwards slightly before we hear the sound of the crash. (00:29:10)
The Second Time Around - S1-E4
Revealing mistake: When Grandad is speaking strangely and telling Del that Pauline has hidden his teeth, you can see his bottom set of teeth.
Chosen answer: An apparent long string of illnesses.