Revealing mistake: In a shot of Duck at the smelter's, a hole is visible on his running board.
Thomas the Jet Engine - S6-E22
Revealing mistake: After Cranky unloads the jet engine, it is already turned on.
Revealing mistake: Peter Sam is already missing his whistle even before it gets knocked off by the branch.
What's the Matter with Henry - S7-E6
Revealing mistake: In a close-up shot, Henry is very dusty, and fingerprints can be seen on his smokebox.
Revealing mistake: When Toby tells the Fat Controller about the broken windmill, his driver's head appears to have been digitally added.
Fergus Breaks the Rules - S7-E18
Revealing mistake: A wire is under Fergus when he arrives at the smelter's.
Revealing mistake: When Murdoch asks Gordon "What decorations will you have, Gordon?" his left eyebrow (viewer's right perspective) is scratched.
Revealing mistake: Salty is missing his rear lamp in the first shot at the docks and a hole is visible where it should be.
Revealing mistake: In a close up of Gordon after Rocky clears the tracks, Gordon has wonky eyes.
Revealing mistake: When Henry arrives at the forest where he finds his lucky trucks, one of the trees is not covered in snow.
Revealing mistake: When Toby asks Thomas if he took on enough water, Toby's eyes are wonky.
Thomas and the Billboard - S12-E1
Revealing mistake: At the beginning of the episode, Henry has Gordon's face.
Thomas Puts the Brakes On - S12-E17
Revealing mistake: When Stanley shunts Thomas into the yard, Thomas is eyeless.
Thomas Puts the Brakes On - S12-E17
Revealing mistake: In the very last shot of the episode, Thomas and Stanley are faceless.
Revealing mistake: In a shot of Gordon arriving at Brendam Docks, only half of his tender is visible.
Revealing mistake: When the elephant is loaded into the truck, the tracks abruptly end behind Charlie.
Santa's Little Engine - S17-E18
Revealing mistake: At one point, the shading effect on Thomas' whistle is not rendered properly, so it appears silver instead of gold.
Revealing mistake: Each time when Thomas takes a shortcut, the points do not change.
Revealing mistake: Duck's footplate clips through the platform at Knapford at the beginning.
Revealing mistake: Some trucks are completely Off the Rails at the clay pits.
Answer: Breakdown trains help the engines back on track.