9. The Magically Unzipping Outfit - Galaxy Quest
Though it's well known by this point that Sigourney Weaver managed to sneak a silent F-bomb into PG-rated sci-fi spoof Galaxy Quest due to some unconvincing dubbing, there's another mistake which was kept in the film with the seemingly sole intent of distracting viewers' attention.
Late in the movie when Jason (Tim Allen) and Gwen (Sigourney Weaver) are about to press the big blue button which will stop the ship from exploding, Gwen's outfit randomly goes from fully zipped up to zipped all the way down, giving viewers quite the eyeful.
The reason for this continuity error is that an additional scene was cut from the sequence during post-production, where Gwen is forced to unzip her outfit in order to distract a group of alien guards.
The genius of the mistake, though, is that it's entirely consistent with Gwen's TV alter-ego Lieutenant Madison, who is depicted on the show as the eye candy member of the crew.
Considering that much of the movie's humour hinges on the actors basically becoming their characters over the course of the movie, it totally fits that Gwen would just randomly unzip her top without any narrative reason to do so.