Revealing mistake: In a close up of Edward, he has Thomas' whistle sound and no tender.
Revealing mistake: When Thomas leaves Dryaw, in the background, the biplane's propeller stops spinning, revealing that the propeller is actually a CD.
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 close up of Gordon after Rocky clears the tracks, Gordon has wonky eyes.
Revealing mistake: When Gordon is being pulled from the pond, in the close up scene of Gordon reversing up the sleeper bed, the front of his buffer beam/running board catches on the upright stake to the right hand side of the worker figure, pulling it back before it rights itself. (easier to see on widescreen version). (00:04:10)
Revealing mistake: In a shot of Gordon arriving at Brendam Docks, only half of his tender is visible.
Revealing mistake: When the passengers lift Duncan back onto the rails, his trailing wheels are still derailed.
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.
Answer: Breakdown trains help the engines back on track.