Revealing mistake: After Kelly tells Big Joe he's going after the gold "with ya or without ya", a soldier in the background walks past a steel tank trap weighing a quarter ton (http://en.wikipedia.org/wiki/Czech_hedgehog). He bumps it with his backpack, and it flips up in the air.
Revealing mistake: At the end of the scene with the destroyed bridge, when Oddball's Sherman drives away, Cowboy is nearly left behind and climbs onto the rear of the tank by standing on a box attached to the rear plating. The next time we see this tank from the rear, the box is gone. It was obviously there only to help Cowboy climb on.