Revealing mistake: In the beginning of the movie when Al Pacino is supposed to be browsing the web you get a quick look at the address bar. It shows the URL to a local .html file instead of a website.
Revealing mistake: In the chase scene in the subway, Napster stops the subway train at the end of the tunnel to block the tunnel entrance. When you see the view on his laptop, the train station CLEARLY has a metal railing. There is no such railing throughout the rest of the scene. (Yes, it's likely while filming that railing was removed to enhance the scene then put back.) (01:27:45)
Revealing mistake: In several scenes of the zombies swimming under water, they are obviously holding their breath. Would a dead zombie need to do that?
Revealing mistake: When Robert Downey Jr. is taking Halle Berry's blood pressure, the needle doesn't move as he pumps the hand inflator.
Revealing mistake: When Dae-su enters the room of one of his nemesis, his computer screen shows information about the stock exchange. The Internet address on the screen is: C:/DocumentsandSettings/[.]/OldBoy/[.], which would be a link to a folder on that computer, not an Internet address.
Revealing mistake: In one of the flashback scenes at the "bunker", a number of the shots fired pierce the sheet metal roof. When they show these holes, you can see fairly bright light coming through. This scene was supposed to be in the jungle during the night. There shouldn't be light streaming in; moonlight is not that bright. It was obviously artificial light used to enhance the scene.
Revealing mistake: When Watson is standing over Jackie's dead body and says "I'm sorry I wasn't there when you needed me most, my friend" you can see Jackie reflected in the TV standing ready for his queue before entering the picture. (00:41:55)
Revealing mistake: When Martin Lawrence was trying to get into his car after he supposedly locked the keys in it, you can see in the shot from inside the car that the door was unlocked. You can tell because the orange-red sticker on the lock is showing, which wouldn't be visible if it was locked. (00:10:50)
Revealing mistake: When the "light rail" vehicle is crossing the bridge, several shots reveal that it is not traveling on rails, but on a metal grating. This is most obvious after the police have stopped it. We see a bridge deck designed to carry cars & trucks (in fact, the police have just driven out on it) with strips of metal laid on the surface to simulate "rails". As others have observed, this was filmed on the wrong bridge; this makes it particularly obvious.
Revealing mistake: When Melanie, Tracy, Evie and Brady are in town, people can be seen stopping to watch the actors/look at the camera. (00:53:35)
Revealing mistake: During the cage fight, Su breaks a man's arm. We can see the break, however we can also see his real arm hidden under his shirt. There is a big lump under the fake arm. (01:01:30)
Revealing mistake: When young Ichi has a "climax" at the end, you can tell his "spunk" is really just white goop and isn't real.
Revealing mistake: When Selene notices the sword laying on the rocks, the sword moves up about two inches between shots, you can judge it by looking closely at the handle of the sword. (01:49:25)
Revealing mistake: During the scene where Lara and Reiss's henchmen are fighting in the lab with the orb, look closely: the computer monitors in the background briefly flicker (as most monitors appear on camera), indicating they were shot in the background. During the close-ups, this does not occur.
Revealing mistake: The video that Bitsey watches at the end of the movie, we see David walk over to Constance's dead body on the floor and Dusty walk away to stage left of the video camera. David then immediately turns around and walks towards the video camera, staring right at the lens. As he walks closer, the camera slightly pans down to keep him in the shot. The problem is nobody is running the camera. It was on a tripod on a table. Dusty would have to have done a quick 90 degree turn, stood on a chair and gotten set behind the camera in a very short period of time - without shaking the table or the camera.
Revealing mistake: When Maggie is chasing after the truck in the light aircraft what appears to be a "pasted-on" face in the cockpit, on closer inspection (with zoom feature on DVD players) is a male pilot flying the plane.
Revealing mistake: When Morgan Freeman is about to take off in the helicopter to chase after the other two chasing Mr. Grey, one of the soldiers who is running to try stop him runs over a small pile of snow. The snow has a very unusual springing nature, obviously the springboard for the stunt, then as a result the soldier falls over.
Revealing mistake: In 1981, when most of the story takes place, the 1981 Dodge Diplomat was the most common police cruiser, but the director of this film chose the 1987 Chevy Caprice Classic.
Revealing mistake: Steve's partner Angela has straight hair, but the stuntlady who doubles her in the city car ride has curly hair. (00:26:35)
Revealing mistake: When Dr. Kendricks closes the eyes of the dead woman, you can see on woman's neck, that she is still breathing. (01:05:10)