Speed (1994)

Revealing mistake: If you look at the missing part of the bridge, and look at the shadow underneath, the shadow is of a full bridge. (01:02:35)

Revealing mistake: In the scene before they jump the gap, they played the film in fast forward to make the bus appear to be going faster. If you watch the police on the truck in the background, they are moving in fast forward as well. (01:02:50)

Revealing mistake: After the first bus explosion when Jack answers the phone, he looks at his watch, which shows 8:05 a.m. If you look closely the watch is on alarm, not regular time. (00:29:05)

Revealing mistake: When Jack and Annie are getting off the bus via the access panel on the floor you can see wheels on the bottom of it. You can also see that Keanu Reeves was replaced by an obvious stuntman. (01:30:00)

Revealing mistake: When the first bus is blowing up, in the shot of the right side of the bus as it's being engulfed in flames, look closely and you'll see the cable attached to the front of the bus, under its bumper, as it's slowly being pulled by the van in front of it (some DVD or Blu-ray versions may have been edited). (00:26:45)

Revealing mistake: At the end, when the empty bus rams the freight plane, the wire pulling the bus can be seen. Most obviously in the low shot shortly before impact, where there are several wires/shadows on the ground leading towards a fixed point in the runway beyond the plane.

Revealing mistake: When the train is sliding along the ground near the end, there are sparks coming from the underneath (supposedly where the metal scrapes the pavement). Look more closely, and you can see that the sparks are coming from a bit of the train that's not touching the pavement anywhere. (01:44:55)

Revealing mistake: In the scene where Jack and Annie escape from beneath the bus via a trap door, the shot of them skidding across the runway shows a ring on Jack's left hand as it is wrapped around Annie. Jack is not married in the movie, but his stunt double must be.

Revealing mistake: As the bus makes the impossible right turn at high speed, you can see the outrigger wheels underneath to stop the bus going over.

GalahadFairlight

Revealing mistake: In the scene where Payne is waiting for the money to be dropped into the bin, he looks through the blinds out onto the street. When he lifts up the blind with his 'bad' hand, you can see his fingers and thumb taped up out of the way.

Revealing mistake: During the rescue of the elevator passengers at the start of the movie, when coaxing the last woman out, there is a shot of the interior of the elevator where you can see the ground through the hole in the elevator floor, even though the elevator is still meant to be on the 22nd floor. (00:16:47)

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.

Revealing mistake: In the scene where Jack has come back into the bus from being underneath it, he is talking to Annie about losing gas, if you watch closely he says "Mac" without pressing his button to call him first, then in another shot you see him press it when he starts talking to Mac. (01:15:50)

The-Immortal

Revealing mistake: When Howard Payne's house explodes, a wire is visible as it pulls back one of the police officers who gets "blown back" by the explosion.

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.

Revealing mistake: The Jaguar owner holds up the piece of paper with "bomb on bus" written on it, then he loses his grip on it, and when the paper lands directly on the bus windshield, the stunt wires are visible at its sides. (00:37:35)

Super Grover ★

Revealing mistake: When Jack is fighting Dennis Hopper on the roof of the subway train, a piece of paper falls off one of them and then stays surprisingly still considering they're on a speeding subway train.

Revealing mistake: When Harry and Jack arrive at the building at the start in the police car, you can see the tire skidmarks on the road from previous takes. (00:05:05)

Craz

Revealing mistake: After Jack has taken command of "Tuneman"s car, in the wide shots of them chasing the bus you can tell it's not Keanu Reeves driving. The stunt driver has slightly longer hair in a more squared crew cut.

Revealing mistake: The Boeing 707 freighter that gets blown up by the bus bomb is obviously a "scrapped" plane (A plane that has lived out it's usefulness and is being readied to be scrapped). One good way of telling this is the plane's exterior shows heavy weathering wear from being stored a long time. But someone told me the way it looks could also be a hasty paint job using ordinary house paint. Either way, still something to look for.