When John McClane discovers Hans Gruber on the roof of Nakatomi Plaza, Gruber cries "Please God NO!.. You're one of them hosta" as he slips into saying "hostages" instead of "terrorists".
The audio is then cut off, and Gruber repeats "You're one of them"
When the SWAT team attempt to enter the building but fail to pick the lock, one member is clearly seen lighting a cutting torch to burn through it. A few scenes later you can distinctly hear a grinding noise, suggesting a drill or an angle-grinder is being used in an attempt to break the lock.
At the end of the film we see the building explode in the distance. The sound of the blast is heard at the same instant as the on-screen explosion, but since light travels far faster than sound there ought to have been at least a few seconds' gap between seeing the explosion and hearing it.
When John is first pursued by a terrorist on an upper storey still under construction, he repeatedly switches a radial-arm saw on and off. You can clearly hear the blade striking a kerf in either the fence or the table. However, when the terrorist later finds the saw, the blade is plainly spinning freely.
When the terrorists' car first draws up at Nakatomi Plaza, the noise from its brakes does not match the movement of the vehicle.
Early in the film, when the technical specialist radios the terrorists in the lorry to tell them that they've seized the reception area, the terrorist who replies keeps the transmit button pressed and appears to speak, yet no words are audible.
When John is first pursued by a terrorist on an upper storey still under construction, he repeatedly switches a radial-arm saw on and off. The very distinct sound of the blade running against either a kerf in the fence or a kerf in the table can be heard. However, when the terrorist later finds the saw, it is plainly evident that the blade is spinning freely.
At the beginning, at roughly 1 minute 27 to 30 seconds, McClane says "okay" but there is a noticeable delay, and the footage clearly appears slowed down, producing a ghosting and/or blurring effect as he moves his head and/or neck.
Takagi points out that any computer information Gruber obtains would be changed "when they wake up in Tokyo in the morning." Japan is 17 hours ahead of Pacific Standard Time, so early evening in California corresponds to roughly midday in Tokyo. The staff would not need to "wake up" at all, since they would already be at their desks.
After Powell had finished sweeping the Nakatomi building to report the 'wild goose chase,' the dispatcher failed to follow proper procedure and did not respond to Powell's transmission when he said, '...everything here is okay, over.' Dispatchers must always acknowledge or repeat the last transmission.
When Harvey at the news desk grimaces in response to Thornberg's 'Eat it, Harvey!', he then gets a five-count signal to go on air. The final two counts (and occasionally the last three) are silent and are never spoken aloud.
Holly's maiden name is correctly recorded as 'Gennaro' in the computer system, but when John taps it on the screen it switches to 'Gennero'. It is also misspelt as 'Gennero' on her office door.
John passes his Beretta to Hans, who at the time is posing as the American Bill Clay. Hans, however, is clearly well versed in firearms. Seasoned users can often tell whether a weapon is loaded merely from its weight in the hand. Hans would therefore realise that John had handed him an unloaded pistol.
During one of the news bulletins, an "expert" suggests the hostages are suffering from "Helsinki Syndrome." The correct term is "Stockholm Syndrome."
Given all his cunning and the meticulous planning he invested in the robbery, Hans ought to have known what Takagi looked like, instead of asking where Takagi was and even walking straight past him.
When Thornburg persuades his boss to go to Nakatomi, his boss instructs him to take lorry 5. Towards the end of the film, as the lorry returns to the building after visiting Holly's flat, it is clearly marked with a 4, identifying it as lorry 4.
When the terrorists first arrive the lorry contains no ambulance, yet towards the film's conclusion Theo is seen driving an ambulance out of it — a continuity error acknowledged by the filmmakers.
The FBI dispatches two helicopters to Nakatomi; however, moments before the rooftop scenes centred on John, the second helicopter vanishes and never reappears.
The orchestra vanishes. They are playing while McClane is driving to the Nakatomi Building, again after he arrives, and once more when the terrorists burst into the reception. Yet when the hostages are rounded up — and later when they are forced onto the roof — none of the orchestra members can be found.
At first John McClane wears a pristine white vest that becomes soiled and bloodstained; before long it is an even brown all over.
When Argyle ploughs into Theo's van, the front of the limousine is left severely damaged. Yet when he comes back through the gate at the end of the film, the same area appears largely intact. (The gate itself would plausibly have inflicted more harm than is shown.)
Before descending the staircase in the lift shaft, McClane (who is meant to be barefoot) is plainly visible wearing shoes as he leaps through a raised service door.
While Hans is impersonating Bill Clay, his hairstyle keeps changing.
Takagi is killed in the boardroom. Young trees are clearly visible beyond the window, and Takagi had already said the building was newly constructed. McClane hurls an assailant out of the window onto Powell's police car. There is no way the trees could have been tall enough to reach the 33rd storey.
After McClane shoots into the air and is fired at but not struck by one of the FBI agents, the other agent, Johnson (the white guy), says "Swing around again - I'll bag this little bastard" and both agents look towards the camera as though the roof were on their left. However, the roof of the Nakatomi building can be seen through the window *behind* them, to their right, and the subsequent jump cut actually shows the building in front of them, not behind.
McClane hurtles through the window on the hose and lands on his back. In the next cut he's lying on his front.
When Karl's brother is tailing McClane on the storey under construction, the stack of plasterboard sheets that John hides behind and that Karl's brother walks around keeps shifting.
As the hostages are escorted up onto the roof, the blonde woman in the grey dress is shown twice walking up the stairs and turning left onto the roof.
Whilst trying to get Al's attention, John strikes the window with a chair but only manages to crack the glass and make a small, head-sized hole (clearly this is safety glass, which will hold firm even when shattered). Yet at the end of the film, when John shoots Hans, Hans falls back against a window that completely gives way, allowing him to fall through it (which, evidently, is not safety glass).
The Christmas tree on the table, behind which Karl is hiding, is already lying on its side before McClane later topples it.
When Sergeant Powell pays for his Twinkies in the shop, the cashier stretches his arm over the counter in one shot; in the subsequent shot he doesn't.
John is shown removing glass shards from his foot in the bathroom; on the wall behind him a bloodstain varies in size between shots as he speaks with Sgt Powell.
Ellis's hairstyle changes between shots while he speaks to John on the walkie-talkie.
After Hans shoots Ellis in the head, shortly afterwards the camera is positioned behind Ellis's head and Hans can be seen through the sizeable hole in Ellis's head; yet later, as Ellis is dragged out of the office, the injury appears merely as a small gunshot wound on his head — the large hole has vanished.
Hans takes over Holly's office, which is down a corridor from the staircase. Later on, towards the end of the film, Holly's office — complete with her family photographs — is shown in a corner beside a stairwell that leads to the 31st storey.
After John suspends Karl by chains and slides him towards the wall, the following shot reveals a staircase behind John, with Karl standing at its top.
After the emergency call is cancelled, the guard goes up to the 32nd floor where John is. When he switches on the lights, the film crew can be seen in the window's reflection.
As John is fighting Karl towards the end of the film, Karl's harness is clearly visible as he is dragged across the room by the chains which are supposedly round his neck.
After John leaves Karl hanging in the roof plant room, in the next shot — as he reaches for his pistol on the floor and checks that it's loaded — either Alexander Godunov or his stunt double can be seen standing at the top of the stairwell behind John, clad as Karl in a black shirt and trousers, watching the take.
Towards the end of the film, as McClane makes his way through the large hall — the very room where the hostages had been held earlier — a shadow of a person can be seen behind the Christmas tree immediately after the tree topples.
Camera shadows are visible at certain points in the film (for example, when John is making his way through the emergency staircases).
SPOILER: As the terrorist discharges the rocket launcher for the first time, in the exterior shot immediately after the explosion (approx. 1:15:00) a cameraman wearing red undersleeves can be plainly seen standing beside the weapon.
On several occasions during radio transmissions on their two-way radios, the characters talk over one another — something that wouldn't be possible with the sort of radios they were using.
At the end of the film Hans is clinging to Holly's wrist by her Rolex (this is mentioned in the dialogue earlier). To let Hans drop to the ground, John flips the clasp on the watch and it comes away from her wrist, allowing Hans to fall. Rolex watches do not have a clasp of that type; their bracelets form a continuous loop and are removed by a fastening that effectively increases the loop's size. In the film the strap is shown as a non-continuous piece.
When McClane contacts the emergency dispatch by radio, the operator's computer monitor displays a telephone number.
The helicopters used by Johnson and Johnson in their rooftop rescue attempt are unmistakably United States Marine Corps gunships. However, deploying the military on US soil to handle a hostage crisis would have required presidential authority to suspend the Posse Comitatus Act.
Nonetheless, the production companies somehow circumvented the Posse Comitatus Act and managed to obtain those gunships for the film.
When John McClane shoots the Italian terrorist from beneath the desk, the bullet holes are visible on the front of his abdomen, whereas they ought to have been on the lower part of his body.
John Phillips is a women's clothing tailor and shop in London and does not make suits. The original script had Hans acquiring his suits from "Paul Smith", a renowned gentlemen's outfitter, which would have been a more accurate detail.
After Hans shoots Mr Takagi, blood and brain matter are spattered across the window behind where he was seated. However, the glass itself remains undamaged, despite the bullet having clearly passed entirely through his head to produce that kind of spray.
Despite John having badly lacerated his feet, it never occurs to him to dress them with bandages to avoid leaving any blood behind. This is illogical, and all the more so because every time he fights or moves he is likely to reopen those wounds.
Notre Dame and USC are shown playing an American football match in daylight, even though it is clearly night in Los Angeles. The fixture is also scheduled on Christmas Eve, which is an odd date for these two sides to play a Bowl game unless both have had poor seasons and are competing in the Christmas Eve Hawaii Bowl.
Early in the film, shortly after the terrorists launch their attack, McClane peers out of a window and notices a woman in the building across the road. However, earlier and later long shots of the building he's in indicate there are no other buildings nearby.
After McClain kills the first terrorist, he attempts to take the man's shoes but finds them too small. He then kills several other terrorists, yet is never shown inspecting their footwear.
When Argyle inserts the cassette into the limousine's tape deck and turns the volume up, he adjusts the 'bass' knob rather than the volume knob, causing the music to get louder.
When Hans gives John McClane the false name "Bill Clay" while they are on the 33rd storey, the camera closes in on the name directory and reveals "Aster" with "FL" listed as 39, even though the Nakatomi Building comprises only 35 storeys.
When Hans watches the TV news clip about the McClane children, he picks up a portrait of McClane with his family and immediately realises that Holly is McClane's wife. One would assume Hans had examined nearly everything in the office from the outset and therefore would already have known her true identity.
The 'terrorists' intend to persuade the FBI to switch off the electricity to Nakatomi Plaza so the vault's lock will open and they can steal the bearer bonds inside. Any electrical system of such critical importance would, however, be connected to a UPS — an Uninterruptible Power Supply — so it would remain operational even if the mains power were cut.
After McClane shoots Tony on the staircase, it was ill-advised for him to confirm a rogue element by sending Tony’s body down in the lift and thereby alerting the other terrorists; he should have concealed the body and made use of his kit.
The terrorists might have come to check on Tony’s whereabouts, but unlikely in force — they would have expected the threat to be the man with the machine gun, ho, ho, ho.
When the terrorists seize the building they switch off the escalators — a pointless action, as a stationary escalator can still be used.
Karl and Tony disable the entire telephone system, while Tony rigs a feedback loop so the intrusion is not registered as a service outage or as tampering with the telecom equipment, and to stop alarms from being triggered and sent to the 911 centre. Fourteen minutes later McClane pulls a fire alarm call point, which sends an alert to 911 despite all the telephone lines having been cut and looped back.
Sergeant Al Powell, talking with another sergeant, says he dislikes that two helicopters are on their way carrying FBI agents. They are shown watching the two helicopters approaching Nakatomi Plaza; although the aircraft are clearly visible, they are depicted circling other buildings and taking far longer than necessary to get to the plaza.
After Hans shoots out the glass and John cuts his feet, leaving them bloodied, Hans could easily have followed John’s blood-stained footprints, caught up with him and shot him dead. It makes no sense that he doesn’t.
"Shoot the glass" underlines how vulnerable McClane's bare feet are to broken glass. Yet on every other occasion his feet and body seem immune to the shards — for example, when he shatters the glass panel to fetch the axe, when he is dragged through broken glass by the falling hose, or when he lies amidst shattered glass to prevent Holly from falling.
John's holster goes missing after he escapes from the terrorists, which is unwise as it contains his spare magazines (which can't be seen on him), and leaving it behind would most likely arouse suspicion.
Clearly a stunt double for McClane (the shoulder tattoo is missing) in the fight against Karl.
While an electricity company employee is telling the city-centre dispatcher to "turn off grid 2-12," he keeps the push-to-talk button held down when the dispatcher replies.
When John reunites with Holly, sheets of paper flutter around them. The documents are meant to be the bonds the gang were trying to steal, but it is clear the pages are blank.
When reporter Richard Thornburg is listening to his police scanner, he hears Officer Powell shouting for backup. At that moment the red lights on the front of the scanner are continuously flashing from left to right. However, on that particular model the lights would cease flashing and remain steadily illuminated on the single channel while it was active.
Clearly the stunt double for John McClane in the altercation with Tony.
When Theo speaks to Hans about needing a miracle, analogue videotape dropouts — clearly visible as flickering horizontal lines — appear over the vault security system graphics that read "Electromagnetic Seal Engaged - No Local Access."
This indicates that the graphics are being played into the monitor on set from tape (most likely a Sony U-Matic or Hi8) and that the tape and/or player had been well used. Such analogue dropouts point to physical tape wear and/or a poorly maintained player.
In the lift, after seeing "ho-ho-ho" printed on Karl's dead brother's shirt, Hans extends his hand and tilts the dead man's head — it blinks when Hans' hand makes contact.
John's holster disappears after he enters the stairwell when the terrorists first arrive. This is unwise because it contains his spare magazines (which are not visible on him), and if the holster were discovered it would most likely alert the terrorists to the presence of an armed person in the building.
When John hurls Karl into the wall on the chain slide, the mortar between the bricks billows into dust.
Shortly after Takagi is killed by Hans, the terrorists set C4 near the roof. One man tosses some up to another, who places it on the steel girder above him. It can be seen almost immediately falling back down, and you can hear it strike the floor.
