Revealing mistake: In the scene where Donna flies as a captain, you can see on the throttle quadrant there are three levers for three engines. There are groups of four dials instead of three for engine temperatures and pressure, and they don't even show symmetric values for similar engines. Furthermore, the altimeter reads over 3000ft, equivalent to a landing in Switzerland or Peru. Finally, there are multiple red and yellow lights on the panel; these colors only come on as a warning like low cabin pressure or engine fire.
Revealing mistake: At several points, there's a really distinct difference in eye color between Mike Myers' (John) real eye and the color contact he has in his other eye.
Revealing mistake: The text of the newspaper article entitled "Stewart Joins Sobieski and Flynn" is about something else other than Ted joining the law firm. (01:20:00)