Continuity mistake: When Dennis Hopper's shooting the shotgun through the lift roof, the number of holes doesn't match the number of blasts. He shoots once and a hole appears. We then see a close up of him and he shoots twice more, but when we cut to the ceiling after the third shot overall, there are only two holes in it. Doesn't seem likely he'd miss the roof at a range of 2 feet.
Continuity mistake: In the scene where Jack is fighting Dennis Hopper on the roof of the subway train we see Jack lying on the top of the train getting punched by Dennis. We briefly cut away, and then back to Jack and the corrugations on the train roof have rotated through ninety degrees.
Continuity mistake: When Jack is running across the street in downtown Los Angeles, in two different camera shots two different red cars are shown stopped in the same place to let him cross the street.
Continuity mistake: When Jack is chasing the bus on the freeway in the Jaguar, an overhead shot is shown of the bus with three cars around it, but in the next shot of the traffic, the road is full of traffic which is surrounding the bus, which is highlighted by Jack having to to swerve around the cars.
Revealing mistake: Before Jack rips the door off the Jaguar, he speeds ahead of the bus and then opens the driver's door at highway speed. At 50 MPH there would be a lot of air resistance, yet Jack opens the door effortlessly.
Continuity mistake: In the shots before the bus blows up the Pacific Courier Freight plane, you can see that the vehicle towing it and the plane itself are no longer moving, as opposed to a couple of shots before this where the tow vehicle and plane are moving at a good pace. You also can no longer see the man who is supposed to be driving the tow vehicle (who might have run for it, but there's minimal time).
Revealing mistake: In the scene right before the bus blows up the "Pacific Courier Freight" plane being towed, you can see the cables on the ground leading towards and underneath the plane, which are used to keep the bus going in a straight path. These cables are also visible in some previous shots before the plane blows up, most notably before the first view of the bomb's speed indicator showing it counting down the speed. If you go frame-by-frame on the close-up of the plane actually blowing up, you can see where it is physically attached to the bus, just behind the front bumper.
Continuity mistake: In the scene where Jack drives the car backwards so he can tear off the door, enabling him into the bus, he slams into a silver car. The very next shot, maybe two seconds later, there is another car driving behind him like nothing happened.
Continuity mistake: Near the end of the film when Keanu Reeves and Dennis Hopper are wrestling on top of the subway, if you watch Keanu's left wrist you notice he is wearing a watch. Yet throughout the scene it is obvious that the stunt double has no watch, because in the extreme action scenes, there are no signs of it anywhere on his wrist.
Revealing mistake: In the scene in the subway Denis Hopper has again used an explosive jacket like that used at the start of the film, which is detonated if the remote trigger is released. However when on the subway train, Denis takes the remote back from Sandra Bullock and it is seen that the trigger is quite obviously released and Denis pushes it back in.
Continuity mistake: When Jack and Harry are pulling people out of the elevator there are two men offering to help the stubborn lady out of the elevator. 2 seconds later there is only one man jumping to get out.
Continuity mistake: In the scene where the plane is blown up at LAX, the intact plane is shown with no mountains in the background. However, the scene showing an exploding plane has a backdrop of desert mountains, presumably Antelope Valley California.