Revealing mistake: When McClane goes into the icy room in the power station, look at the pipe to the side of the acrobat: it's in shot a few seconds and you can see that the writing on the pipe is reversed, revealing that in the editing room, the shot was flipped.
Revealing mistake: Near the end of the film, when Bruce Willis is trying to escape into the Metro station, he swipes his fare card through the turnstile reader upside down - you can see the magnetic strip is visible above the slot. It still works anyway. (01:45:30)
Revealing mistake: When the couple in the truck are driven off and down the side of the mountain the direction of the truck does not match the direction he steers the truck.
Revealing mistake: When Jules and Vincent are riding in the car during the "Royale with Cheese" conversation, it is possible to see the reflection of their car in the background, being towed on a trailer. (00:07:05 - 00:08:00)
Revealing mistake: When Mike Douglas makes Dr. Sacks answer his cell phone, you can see that Sacks is wearing a wedding band although he wasn't married.
Revealing mistake: As the gang is being chased through the "96th Street Station", you can see the true station name "Hoyt" (as in Hoyt-Schermerhorn Sts. Station) on the outer station wall. (00:42:50)
Revealing mistake: Just before A-Wax kills the guy in the red sweatshirt, you can see the squibs bulging on his back, underneath the victim's clothing.
Revealing mistake: When the Grand Ville turns onto the street where the children are playing, it clips a parked car as it makes the turn. This is the same car that later gets its driver's door ripped off by the Grand Ville just before the police give chase. It was repainted red for the second scene, but note the same dent in the right fender as before.
Revealing mistake: During the police chase with Gabriel on his motorcycle, he stops and turns to start shooting at one of the cops. By appearances, Gabriel is using a standard Glock which had a magazine capacity of 15 rounds. He has no extensions on it at all with the handle and magazine visible. Yet he proceeds to fire the gun 33-35 times at the cop car without reloading and in continuous fire. (00:57:55)
Revealing mistake: In the scene where the bodies are found in the river, Tom Berenger yells, "Sarah". As he looks down the river in the "wilderness" a logging truck can be seen driving down a road.
Revealing mistake: It's an obvious rubber dummy when Chavez cuts off Juarez's leg. (00:43:30 - 00:44:05)
Revealing mistake: When the FBI agent is in the room of the court medic to get the cause of death, in several shots the sliced up corpse is breathing. (00:27:00 - 00:29:30)
Revealing mistake: When Kato is driving home after the argument with Britt about making coffee at the office, Kato is jerking the steering wheel randomly like a child pretending to drive despite it seeming they are just driving straight down the road. (00:56:30)
Revealing mistake: When Mr. Green pulls out of 28th Street, we see him disengage the "Dead Man's Feature" (by pressing down on the throttle with his hand). However, he does not actually move the control lever to make the train move. In that position, the train is at "idle" and will not accelerate.
Revealing mistake: When Two-bit Mathews returns from the hospital gift shop with a copy of "Gone With The Wind", he hands the book to the nurse asking her to make sure that Johnny gets it. The book he hands her is an obviously used paperback with the upper front top right corner and pages all bent back. Shouldn't a gift shop sell NEW items? The book is only shown from the non-title side so they could have used any paperback for the prop as long as it looked like it wasn't several decades old.
Revealing mistake: In the sequence in which Antoine Sartain throws a flare to set fire to the car with the two dead bodies, you can see it hit the floor from the left, but the fire comes from a complete different angle. (00:22:50)
Revealing mistake: In the gun battle following the bank robbery, Drucker fires his shotgun at Cherrito. A female pedestrian in the background (apparently unaware she's in the shot) can be seen acting casually, without any reaction to the gun battle taking place.
Revealing mistake: When Hamer goes to the gun store and obtains all of his weaponry, the gun counter guy and boy carry the weapons out to his vehicle. The weight of the weapons would be too much for one to carry all at the same time and the boy is supposedly carrying that large box of ammo, which would have contained over a thousand rounds, but he's carrying it like a box of feathers.
Revealing mistake: When John Garfield is trying to stop Lana Turner from calling the District Attorney, Garfield holds the receiver up in the air off the hook. Then the phone rings. But a phone cannot ring when it is off the hook.
Revealing mistake: Towards the end, Jake Gyllenhaal is browsing the internet on a computer running Windows 7...despite the "no network" notification icon at the bottom right of the taskbar. (01:25:05)