Revealing mistake: When the armoured truck hits the first parked car you can see the smoke appear at the side of the car and a jet of smoke when it flips from the air cannon.
Revealing mistake: In the opening chase with the armoured truck it comes up behind a blue car that is already dented on the near side, which is the side it slides round to so the truck hits it. It then gets pushed onto a silver van that is completely wrecked from previous takes.
Revealing mistake: When Yuri Komarov is on the phone with his daughter, the screen on the phone is the dial screen rather than the on-going call screen. (00:34:10)
Revealing mistake: When the armored truck flies through the air and smashes into a concrete pipe that is being hauled by a yellow truck, there is a shot from in front of the yellow truck. You can see there is no driver. (00:28:55)
Chosen answer: No. Bruce Willis (and thus, John McClane) is left handed. But guns are mostly designed for right handed people, so when he isn't holding a gun modified for him, it's easier to use it with his right hand.
Friso94