Revealing mistake: The rails to the buffers are broken as Toad leaves the siding.
Revealing mistake: When Toad switches lines to avoid Gordon, the track ends in bushes.
Revealing mistake: When Gordon puffs into the ditch his face looks wonky and wires are visibly attached to his cab.
James and the Trouble with Trees - S5-E5
Revealing mistake: In the end of the episode, you can see James doesn't have his face fitted on correctly, as the gap between it and his eyes appears to be exposed.
A Bad Day for Sir Handel - S4-E6
Revealing mistake: When Sir Handel derails, you can see a small rod sticking up out of the ground from the tracks.
Revealing mistake: When Samson crosses the Vicarstown Bridge, there is no shadow effect on his face.
Revealing mistake: When Gordon falls into the ditch, wires under his cab are visible.
Revealing mistake: The old engine's model, who fell off the bridge, was actually Skarloey's, as some red paint can be seen.
Revealing mistake: In a shot of Duck at the smelter's, a hole is visible on his running board.
Revealing mistake: When Toby tells the Fat Controller about the broken windmill, his driver's head appears to have been digitally added.
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.
Revealing mistake: In a close up of Stepney at the beginning, his lamp iron has a burn mark.
Revealing mistake: When Stepney is returning home through the fog, the source to power his lamp is visible.
Revealing mistake: The end of the set is visible in one shot at the quarry.
Revealing mistake: Duck's footplate clips through the platform at Knapford at the beginning.
Revealing mistake: Before James collides with the tar tankers, he is already covered in tar before he actually hits them.
Revealing mistake: When Thomas collects Rocky, the points are set against him. This also happens when Percy enters the siding.
Thomas Puts the Brakes On - S12-E17
Revealing mistake: When Stanley shunts Thomas into the yard, Thomas is eyeless.
Fergus Breaks the Rules - S7-E18
Revealing mistake: A wire is under Fergus when he arrives at the smelter's.
Answer: He was in the water.