Continuity mistake: Thomas appears to be damaged and dirty after his accident but in the final scene, he is undamaged and clean.
Revealing mistake: Max's wheels can be seen moving backwards when he is actually driving forwards. Also, both Max and Monty's steering and wheel speeds are out of sync with their movements. These events happen throughout the episode.
Other mistake: Oliver's arm is too tall to fit under the bridge.
Other mistake: Thomas has two side rods when he crashes into the pile of dirt. The duplicated side rod moves even though Thomas' brakes are applied.
Answer: Breakdown trains help the engines back on track.