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.
Peter Sam and the Refreshment Lady - S4-E7
Other mistake: In two shots shown at the beginning, Henry is wearing Gordon's upset face mask.
Other mistake: After Toby breaks down, James pushes him directly to Knapford Station, not to the Works as it is said.
Other mistake: When Percy meets Thomas at Elsbridge Station, he has a water line across his boiler, even though the water only came up to his footplate.
Horrid Lorry - S5-E2
Continuity mistake: When Lorry 1 returns after falling into the sea, he is covered in algae and seaweed even though he wasn't submerged. He gains some more of it when Thomas sees him.
Factual error: The dam was built concaved from the water it holds back, but it would have been built convex in order to do so.
Other mistake: Edward is wearing James' sad face mask when he approaches the water column.
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.
Continuity mistake: Throughout Season 4, Henry is painted in two different shades of green.
Character mistake: On his way back to the sheds, Sir Handel goes through a red signal.
Revealing mistake: When Thomas collects Rocky, the points are set against him. This also happens when Percy enters the siding.
Visible crew/equipment: When Gordon, Thomas and the express round the bend, a camera tripod is visible on the left side of the screen.
Visible crew/equipment: In a close-up of Toby, you can see a hand reflected in his left window (viewer's right).
Wrong Road - S2-E22
Character mistake: The narrator refers to the brake coach as the guard's van.
Continuity mistake: Thomas says that Mavis and Cranky never make mistakes, but they have in "Mavis" and "No Sleep for Cranky."
Thomas Puts the Brakes On - S12-E17
Revealing mistake: When Stanley shunts Thomas into the yard, Thomas is eyeless.
Character mistake: The narrator says that the passengers covered their ears at the station, but no one is covering their ears, except Sir Topham Hatt.
Percy Takes the Plunge - S2-E11
Deliberate mistake: When Percy is being loaded onto the flatbed, Diesel appears, but he is not introduced until "Pop Goes the Diesel" (episode after this). This is likely because "Pop Goes the Diesel" was produced before this episode.
Suggested correction: There is nothing in the show suggesting that the episodes are shown in chronological order.
Continuity mistake: Thomas was pushing 4 trucks and a brake van, but when the trucks are laughing at Thomas, there are 2 trucks and a brake van. A truck also gains a face.