When bad guy Joe Beacom approaches the locked door to the tunnels, all four panes of glass in the door are intact. In the next shot, shot from *inside* the tunnels, one panel is broken, and Beacom reaches through that pane to open the door.
When Joyce and Calhoun are having their conversation in the café, the amount of drink in her glass changes between shots.
During the chase on the elevated train, portions of the background rear projection that can be seen through the windows of the train are reversed, flipped so that the lettering of signs is backwards. Probably this was done to match the interior angles in the train that had been filmed.
When Joe Beacom peeks out of the 'Scenic Route' sign before trying to collect the ransom, a black board is moved alongside the camera and can be seen just before we see Joe inside the sign.