You Gotta Lose This Job - S3-E7
Visible crew/equipment: When 'Hannah' and Lilly walk into Rob Reiner's office, the multiple head studio lights are reflected on Hannah's large black sunglasses.
Revealing mistake: In the opening credits, Beefy Bert has a different hair colour to what he has in the actual episodes. This was not included in Series 3.
Continuity mistake: The scene where Dr. Denman captures the mermaids and they fight back with their powers. Emma's facial expressions changes between cuts. (00:07:15)