Revealing mistake: When Colin plays basketball he dunks the ball several times, but if you look carefully you'll notice that in some shots it's a stunt dunking for him who's taller.
Revealing mistake: As Rob, Hud, and Lily are rescuing Beth from her apartment, the view outside the window is tilted roughly 45°. This is due to Beth's apartment building being partially collapsed against another building, demonstrated previously by an exterior shot. However, the characters are moving within the apartment with no difficulty or apparent change in gravity, even though they should be struggling to remain upright in a significantly tilted apartment. This makes it clear that the scene outside has been added using chroma key technology, and the camera has simply been tilted to create the illusion that they are on an angle. (01:01:30 - 01:01:52)