Thomas and the Missing Christmas Tree - S2-E26
Visible crew/equipment: In the scene of Donald and Douglas going out of the yard, a camera tripod can be seen in the top left corner.
Wrong Road - S2-E22
Revealing mistake: When Gordon says, "I am Gordon! Stop! Stop!", his eyes are wonky.
Other mistake: The Breakdown Train to the left, in the opening scene, is derailed.
Wrong Road - S2-E22
Revealing mistake: Wires to power the lamps are very visible on Gordon's and Edward's buffers, and bulbs are also sticking out from both their lamps.
Trivia: When Bill and Ben find Boco, there's a soup can on the left of the screen, dressed to be part of the set like a large oil drum or similar.
Visible crew/equipment: When Bill and Ben go by a level crossing, the top of the set is visible.
Answer: Breakdown trains help the engines back on track.