A lot of the film was filmed in London, rather than New York. If you watch carefully in some scenes, you can see architecture and trees that are obviously British. The lighting is also a giveaway. My girlfriend said she saw a Ford Capri in the background in one shot.
Among the many errors in this film that I'm sure you'll have fun spotting are the teeth (which is physically impossible) and the rocket launcher at the end (which would have injured Kersey and Shriker at the very least, given the proximity they had to the explosion). There are many instances of 'magic bullet' syndrome (bullets swerving around corners), and a knife-proof/bullet-proof vest (which is sadly impossible). Also there are at least two unexploded 'bullet' squibs clearly on view. Can you spot them?
Contributed by: Joe Sherwood
Near the beginning of the movie, some guy breaks into Charles Bronson's car and vandalizes the dashboard area. Later on in the movie, Bronson is shown getting in the car and driving off with no obvious damage!
Once the 'teeth' plank shoots up, look closely in the mirror, you will see the camera man...