Revealing mistake: When Percy is at the "backing" signal, his cylinder is sagging.
Audio problem: Edward has Thomas' whistle sound when he first sees Trevor and when he approaches Wellsworth Station.
Continuity mistake: When Emily and Whiff pull the rubbish trucks away, Whiff is coupled up to Emily, and Emily is coupled up to the trucks. When they pull them away, their buffers are separate.
Revealing mistake: When Edward is at the last station, his whistle is crooked.
Continuity mistake: At the beginning, Edward is pulling 5 cattle trucks. When he approaches the cows, he is pulling 4 cattle trucks.
Continuity mistake: Gordon's express train has 1 composite coach and 2 brake coaches when he passes through Wellsworth station. When he crosses the viaduct, he has 2 composite coaches and 1 brake coach.
Revealing mistake: After Gordon stops on the bridge for the cow, his wheels keep moving for 3 seconds.
Revealing mistake: When Percy stops on the bridge, white glue is on his middle lamp iron.
Continuity mistake: Gordon can be seen next to Edward when Edward says "two big engines afraid of a cow?", but Gordon should have been on the turntable.
Revealing mistake: Edward has wonky eyes in some scenes.
Other mistake: The episode's title in the original PBS Broadcast version is "The Old Iron Bridge" but the bridge was made of wood.
Thomas, Percy and the Coal - S2-E1
Revealing mistake: In some shots of Thomas and Percy, both engines have wonky eyes.
Thomas, Percy and the Coal - S2-E1
Revealing mistake: When Toby pulls Annie and Clarabel, the latter coach has a loose roof.
Thomas, Percy and the Coal - S2-E1
Continuity mistake: When Thomas is being covered in coal, he is dirty in some shots, but in other shots he is clean.
Revealing mistake: Each time when Thomas takes a shortcut, the points do not change.
Factual error: When Bertie finds Thomas derailed, Bertie is on the wrong side of the road. The UK drives on the left. Also, Thomas runs under North American directional rules at the beginning and end of the episode.
Character mistake: UK Only: When Thomas comes back to Annie and Clarabel, he calls the latter "Carabel."
Continuity mistake: Gordon's connecting rods change position after he pulls Thomas out of the mine.
Character mistake: Black smoke comes out of Thomas' funnel 50 seconds before the narrator says so. (00:03:40)
Character mistake: In the trivia game on the "On Site With Thomas" DVD, Monty's name is misspelled as "Monte."
Answer: Breakdown trains help the engines back on track.