Thomas' Christmas Party - S1-E26
Revealing mistake: In the very last shot of the episode, loads of wires are visible in front of the engines and behind the turntable.
Revealing mistake: At the end, when Thomas backs some coaches into the station, he starts moving after 3 seconds the camera starting rolling.
Revealing mistake: When Thomas passes the leveling crossing for a second time, the cars at the crossing have no drivers.
Revealing mistake: When Thomas goes back to the station to try again from the signal, when he starts, the steam is coming from the track and not from Thomas.
Revealing mistake: When Thomas passes a yard with a black car and a red car, you can see tyre marks on the ground from previous takes.
Revealing mistake: Just before Thomas goes over The Switch, his left eye is uneven and then when he crosses The Switch, it readjusts itself.
Revealing mistake: When Thomas leaves the sheds, his driver doesn't have a face.
Revealing mistake: At the beginning of the episode, the end of the set is visibly reflected of Gordon's smoke box in a close-up of Gordon.
The Runaway - S2-E10
Revealing mistake: When Thomas' fireman is ill, you can see a brief flash of red outside, meaning it's James. (Note: same footage from Old Iron).
The Runaway - S2-E10
Revealing mistake: When Duck comes to Terence's field, the end of the track leads right into the bushes right behind duck.
The Runaway - S2-E10
Revealing mistake: When Duck is happy at the beginning, the breakdown train's buffer on the right is broken.
Edward, Gordon and Henry - S1-E4
Revealing mistake: When Gordon passes a signal, the track under him wobbles.
Thomas, Percy and the Dragon - S3-E7
Revealing mistake: When Thomas asks Percy about the guard leaving the light on, Thomas' right eye jitters.
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 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.
Answer: He was in the water.