Samson at Your Service - S18-E24
Revealing mistake: James's chassis is incorrectly positioned when Samson passes him.
Visible crew/equipment: When Stepney puffs through the fog after dropping off the stone loads, studio equipment can be seen in the top left corner of the screen.
Visible crew/equipment: When Thomas says to Emily, "Give them back!", studio equipment is visible on the top-right corner of the screen.
Answer: Breakdown trains help the engines back on track.