Continuity mistake: Right before they rob the police car, a Boeing 747 (four engines) is seen in shots of the plane coming into land. When the plane is shown from behind, it is a Boeing 767, with only two engines and fewer main landing gears. (00:30:10)
Factual error: Fitch, who professes qualifications in biology, genetics and biochemistry, says that they made Sil female because she's a natural predator and so she'd be more docile. He should retake his finals. In every single species of predator on earth - every single one - the females are the hunters, aggressors and killers. The males may be socially dominant but they are the 'docile' ones. There are no exceptions - and no human DNA was used to create Sil - they used synthetic DNA based on the instructions transmitted to them.
Other mistake: When Somerset goes back to the man's house alone, he cuts a sticker on the door with his switch-blade to get in. The first error is the sticker is on the inside and it says "Keep Out." The best part about it is the door opens inward. How did they put the sticker on the inside and then exit? (00:20:45)
Revealing mistake: The kid in the wheelchair is playing a Game Gear with no game in it.
Factual error: No electricity, yet the washer is running.
Continuity mistake: When the two female characters enter the fancy hotel room, they make a point to say they will only be there for a couple of minutes. It is daylight when they go in. The visit is cut short (the one that's supposed to be a few minutes long) because of a gun battle in which one of the women dies and the other escapes. The escaped one gets out through the roof into an evening's sky. There's still light visible, but for a visit that lasts all of 4 minutes, it's far too quick a change. (00:23:00)
Continuity mistake: When Johnny Cage is fighting Scorpion, and he does his human spear, Johnny runs until he stops at the tree. The spear then catches up, and becomes wrapped around the tree in front of Johnny. When the camera changes view, the spear is just leaning on the tree. The camera changes view again and the spear is wrapped around the tree again. When Scorpion pulls the spear back, it goes straight back, and doesn't unwind around the tree.
Continuity mistake: When the white boy is standing outside the car talking to the gangbanger inside the car, the gangster's sunglasses disappear depending on the camera angle.
Continuity mistake: When the incomplete second EAM is shown in the movie for the first time, its subject line states "nuclear missile launc..." However, when this same message is finally received at the end of the movie the subject line states: "terminate launch all missiles". If the first one had been consistent with the second this would have made quite a difference. (00:55:45 - 01:45:25)
Factual error: When McClane and Zeus take the little hatchback from the bank location, they run up the ramp by the Brooklyn Bridge and McClane looks to see the dump trucks aren't on the bridge. Zeus then spots them on FDR Drive and they speed off down the ramp to FDR Drive. The ramp they were on doesn't connect to the ramp they took to give chase. It only heads towards City Hall or over the bridge. They'd have to take the Civic Center ramp, do a u-turn under the Brooklyn Bridge approach then head back up the ramp to FDR Drive.
Plot hole: When Charlie sets out to hijack the money train, he jumps off the platform onto the tracks as it arrives, in plain sight of the driver and other passengers at the station, and only puts his mask on once he's in position on the tracks. The train conveniently stops right over top of Charlie, allowing him to enter through the conveniently-placed grate on the train's floor. (01:17:15)
Revealing mistake: When Two Face and Riddler enter Wayne Manor, and knock Alfred down. Alfred, unconscious, pushes the dinner tray aside, so the thugs can carry him into the closet. (01:27:55)
Continuity mistake: Stallone is eating a banana when he is on the computer in the Mariott. He takes a bite and the banana is smaller, then in the next shot it is bigger again.
Factual error: The suits worn by dangerous disease researchers would definitely never tear if the hose was pulled.
Other mistake: When Michelle Pfieffer hands out menus for the restaurant in the class, they all read them out loud in English. Then when she takes Raul there, he says he can't read it because it's in French.
Other mistake: At the end of the first movie Rybak is a Chief (E7), and he is a retired Lieutenant (O3) during this movie. Assuming he got commissioned to Ensign (O1) immediately after the events of Under Siege, it would take a minimum of 42 months to be promoted to Lieutenant. This movie takes place within 4 years of the first movie, because Admiral Bates is still the Chairman of the Joint Chiefs of Staff. The picture of Rybak in his Lieutenant uniform is at least 5 years old according to his niece. None of these timelines make sense for the rank he is in the movie.
Other mistake: After the post-bank robbery shootout, a TV reporter is heard describing the shootout as taking place in a "small southland neighborhood." But earlier one of the detectives was heard ordering road blocks at Flower and Figueroa, meaning the gun battle occurred in Downtown Los Angeles. Hardly a small neighborhood.