Revealing mistake: When the ship is about to leave, in a close-up one can see the sky and clouds are a painted backdrop: no perspective at all, the clouds inches away and at waist level. (01:01:33)
Revealing mistake: In the scene out West with the buffalo, notice the car driving in the distant background.
Revealing mistake: When Passepartout is on top of the train an arrow hits him but wobbles and bounces off him revealing it's a rubber prop.