Revealing mistake: When Henry passes under the bridge, a tree shakes, giving the illusion that the stones were thrown. When in reality, Henry actually ran right through a low-hanging branch.
Revealing mistake: When Gordon falls into the ditch, wires under his cab are visible.
Thomas and the Breakdown Train - S1-E7
Revealing mistake: Thomas is taking on water in the opening shot, but his water cap is closed.
Answer: Breakdown trains help the engines back on track.