Continuity mistake: Takagi is sitting on the chair facing the door of the room when he is shot. In the next scene, the same door is splattered with blood, yet the glass structure which should be splattered with blood should be the glass window behind Takagi, not the door which he is facing. (00:30:15)
Continuity mistake: When he's climbing down the vents, the strap unties, and Bruce Willis falls. He misses the vent he was reaching for, and falls past the next one, so we assume he catches the third one down. However, after he flicks off his lighter, the camera pans up from the lit vent to Karl, and we can see that he somehow grabbed and climbed into the vent he definitely fell right past in the shot from above. (00:48:30)
Continuity mistake: At the start in the limo, when Argyle is listing all the features of the car, the bear is dead centre of the back seats. The very next shot is in the rear view mirror, and the bear's now over by the window. (00:06:00)
Continuity mistake: When the terrorist Karl is about to kill the man in the front desk, his fringe changes from neat and combed to slightly messy from one frame to the other.
Revealing mistake: John McClane stands in a little pool when the helicopter falling from the roof explodes outside and the windows shatter. In a short shot you see that this man is definitely not Bruce Willis. (01:52:50)
Plot hole: After they shoot the glass and McClane escapes, the terrorists all just leave. There are limited ways out of the room, there must be a blood trail over the glass, he's moving slowly...and they let him go.
Continuity mistake: When Powell's police cruiser is first fired on, he accelerates in reverse quickly. The first obstacle he hits completely destroys the right-hand side tail light assembly. Subsequnt shots of the car show the tail-light to be totally intact again. (00:55:05)
Visible crew/equipment: When Al goes into the lobby of the building, he walks over to a large reflective marble counter. If you look at this counter you can very plainly see the reflection of a large metal stage lamp hanging right over the actors' heads. (00:52:25)
Revealing mistake: When John fights against the blonde German thug, Bruce Willis' stunt and the thug's are very noticeable: different body build plus darker and longer hair in the case of Willis, and bulky wig in the case of the German. (00:35:21)
Visible crew/equipment: When one of the terrorists enters an abandoned floor, logically the floor should be empty, but you can see the casting crew in the reflection of the windows. (00:35:00)
Factual error: A few of Gruber's henchmen set up the rocket-launcher to blast the armored police vehicle. As one of them swings the legs of the launcher down, another uses a 'Hilti' gun to anchor the leg in place. A 'Hilti' gun is a construction device that uses gunpowder (usually a .22 shot) to 'blast' a nail into very hard material such as concrete. With the model they're using, the nail has to be manually loaded into the front of the gun for each shot before it can be used, however the guy using the gun never loads a nail into the gun. As it is, the result would be worthless.
Suggested correction: Hilti sells powder actuated fastening guns with collated fasteners and gunpowder shots lined up. Usually one can fire 10 rounds in a magazine. The gang would have probably selected such a model for this feature.
But that specific collated gun was not the one they were using.
Continuity mistake: When Powell is driving his cruiser in reverse to get away from the bad guys shooting at him, several shots show a full roll-cage in the car which is not there in any other scene or close-up of the interior. (00:55:10)
Visible crew/equipment: Everyone is surprised when Karl is alive at the end of the movie because he appeared to be dead when hanging by the chain that McClane had wrapped around his neck. However, if you look at the back of Karl's head during the entire scene, you can see the safety wire coming out of the back of his shirt that holds him up. No wonder he survived. (01:48:45)
Character mistake: An unloaded automatic pistol is much lighter and balanced differently than a loaded one. When McClane hands "Bill Clay" (Gruber) the empty pistol, a terrorist of Gruber's credentials should pick up on the odd balance (I notice that difference, and I very rarely even pick up a gun).
Suggested correction: This presumes that a person can notice the difference between a fully-loaded pistol versus a pistol that is empty, which makes sense. However, it would be much more difficult for a person to tell that a gun is completely empty versus one that only has one or two bullets loaded. Since Gruber has no way of knowing his ruse didn't work, he doesn't believe McClane would have given him a completely empty gun. He obviously believes there is at the very least one bullet in the gun. He's not planning on getting into a shootout with McClane, he is just planning to threaten him and he certainly doesn't need a fully loaded gun to do that.
Suggested correction: It's easy to tell the different between the weight of a loaded vs. unloaded pistol, but given Hans had never held the pistol before, he had no way to compare the weight. Unless he regularly handled that particular model of pistol (unlikely, given his pistol is a completely different make and model) he would have no point of reference.
Factual error: The rocket-launcher used to destroy the LAPD Armoured car appears to be a French 'MISTRAL' infra-red homing, man-portable surface-to-air missile that is meant for shooting down aircraft and is not designed for a surface target role. Even if the missile seeker could acquire a surface target like the armored car as a correct infra-red signature (required before it will fire), its flight profile would not be suitable for attack and it would probably not even arm the missile warhead at such a close distance. The missile is also not re-loadable in the manner shown.
Visible crew/equipment: When McClane is crawling under the long table to get closer to hear the terrorists' conversation, you can see the reflection of the camera operator's legs following along with him on the table base. (00:29:15)
Character mistake: After the police scanner broadcasts the shooting at Nakatomi Plaza, reporter Richard Thornburg starts begging the station producer/director for a van and cameraman. This is as the evening news is about to go on the air. The floor manager is counting down, "We are on the air in, four, three, two, one...." as he is giving the hand signals to the news anchors. On a real television set, the verbal count would end at three and the mikes would go live. In this case, the floor managers "two, one" and all other words spoken after "three" would be heard by the "at home" audience. (00:58:45)
Audio problem: Just after Hans addresses McClane by his name over the radio, we can hear Powell say, "Better get ahold of someone at dispatch," but his mouth movements don't match what we hear. (01:18:50)
Factual error: When Willis kills the terrorist and throws him out the window onto the police car, the body lands on the windshield, and it shatters into little bits. The windshields on 80's cars were double paned with a thin, strong plastic between each pane, to keep them from breaking into little bits in accidents. Only the side and back windows would shatter like that. (00:54:45)
Continuity mistake: In the scene where Al asks John if he has any kids of his own, John pulls out his wallet with a picture of his family. He is holding the radio and the wallet, but when it cuts to John's "Jungle Gym" comment, both his hands are on the wallet. It then cuts to John again holding the radio and the wallet. (01:16:35)
