Continuity mistake: When Norwood and McMahon break out their maps after hearing about the gap, their platform truck passes a large overhead freeway sign on the right, as seen in a rear window reflection. But a second later, when McMahon insists that the freeway is finished, the sign is roughly 100 yards away instead. (01:02:40)
Continuity mistake: At some point before the bus slams into a tow truck and sends a car flying, a large pile of shrubs appears on the curb's edge near the bystanders who start running for cover. (00:46:30)
Visible crew/equipment: As Jack inspects the bus's speedometer for signs of tampering, a camera can be seen in a reflection on the window to Annie's left. (00:44:35)
Revealing mistake: In the shot where Jack and Harry are descending a ladder to the stranded elevator, we get a good look at the elevator shaft and its surroundings. Upon closer inspection you'll notice how the lowermost section of the shaft is actually a mural - given away by the shadows cast upon it. (00:09:20)
Continuity mistake: In the cafe, when saying goodbye to Bob, Jack's coffee cup changes hands between shots. (00:27:20)
Continuity mistake: In Jack's first attempt to stop the bus, he runs alongside it waving his badge. Between shots, his badge switches from right hand to left (before he turns around to shout "Stop" at oncoming traffic). (00:34:50)
Revealing mistake: A large crowd of onlookers is visible on the highway overpass in the background as soon as Tuneman props himself up in the driver's seat after crashing into the water barrels. (00:40:10)
Visible crew/equipment: As Harry walks out of the office after telling his colleagues to search for their mystery bomber via pension fund files, a boom mic pole is reflected in the left window when he says, "I've seen this a**hole." (00:55:25)
Continuity mistake: When the bus passengers notice Tuneman's Jaguar approaching, watch how Stephens (the tourist wearing a blue shirt and sunglasses) changes his position between shots. From the outside we can see him minding his own business and facing the front of the bus at first, possibly reading a book on his lap. However in the following shot he's suddenly got both arms leaning over the seat back and his head turned left. (00:36:25)
Visible crew/equipment: When Jack is trying to pry open the subway train's doors, a boom mic can be seen mounted on the car's interior, suspended from the ceiling. (01:40:30)
Continuity mistake: In the scene where Jack pulls a gun on Tuneman, watch as Tuneman's hands change positions on the Jaguar between shots. At first he grabs the top edge of the windshield when pulling himself up to switch seats, but then his hands are placed much closer to the windshield's center all of a sudden. (00:35:10)
Audio problem: When Ortiz tackles a criminal in the bus aisle, a gun fires and injures Sam, but the blast can be heard a split second after the trigger is pulled. (00:41:45)
Visible crew/equipment: During the passenger transfers at LAX, a cameraman is visible through the bus doorway two shots before Annie glances over her right shoulder twice. (01:27:35)
Visible crew/equipment: When Jack is running alongside the subway train trying to find a way in, a camera and its operator can be seen on the window's interior reflection. (01:40:20)
Visible crew/equipment: When Jack's Bronco weaves across two lanes of traffic on the highway seconds before throwing it in park to catch up with the bus on foot, a camera can be seen, mounted in the Bronco's back seat. (00:34:15)
Continuity mistake: When Payne is about to board the subway train with Annie, he fires warning shots into the air and she ducks her head in response. But she repeats the same action in the next shot. (01:39:30)
Other mistake: The bus is supposed to maintain a speed higher than 50 mph to avoid disaster. But at one point where the baby carriage full of cans falls to the pavement and starts tumbling we can see part of the bus in the background, slowed to a crawl and certainly not traveling at least 50 mph. (00:50:20)
Continuity mistake: When Payne is in a hideout watching the news unfold on numerous TV sets, he hears one reporter mention that a Los Angeles police officer (Jack) boarded the bus from a moving car. Right here we can see a reflection of Payne in the TV screen, which shows him placing his right hand over his mouth. In the following shot of Payne's face, where he says "Oh would that be you Jack?", his hand isn't anywhere near his mouth. (00:44:20)
Continuity mistake: When Tuneman realizes that he's about to crash into some barrels of water near the exit, he ducks for cover but, in the next shot, we see him sitting upright again. (00:40:00)
Continuity mistake: After telling Tuneman that he needs to board the moving bus, Jack pushes the Jaguar several car lengths forward so that he'll have ample distance to smash the door off. Meanwhile, we can see dotted white lines on the pavement between the Jaguar and the bus. But look over Jack's shoulder as he says "Are you insured?" and notice how two pairs of solid yellow lines have momentarily taken place of the white ones. (00:39:05)
Answer: Ventilation shafts or roof panels.
Toolio