Plot hole: Had one or more locomotives coupled onto the real runaway's front engine, or even just been pushed by it, anyone aboard the "rescue" engine could have just walked to the unoccupied ones and shut them down - no copters or fireballs required.
Plot hole: In the end, all they have to do is ask the President, when he's conscious (Liev didn't kill him; he just knocked him unconscious), who killed everyone in the control room and nearly killed him. He would know who the traitor is and it's not Salt - when they look back at the facts, they'll see how Salt only killed when she absolutely had to, and how she saved lives and stopped a 3rd world war.
Continuity mistake: Right after Bennett takes off in the plane, Claire throws a gun to Alice. Between the slow-motion shots, the gun switches position in mid-air before Alice catches it. In the shot of Claire throwing it, the barrel is facing to the right, meaning that it should be facing to the left in the shot of Alice catching it. But it still faces the right when she does. (00:58:30)
Continuity mistake: After being chased by soldiers after talking to his uncle, Dastan gets into a swordfight with Garsiv. As soon as it starts, Garsiv hits a pillar with his weapon knocking a significantly large chunk and a another smaller chunk out of it. In the immediate shot, the size and locations of the two chunks differ.
Factual error: On the cliff top before the battle on the beach, you are treated to a lovely if fleeting glimpse of wind farm turbines, not really fitting for the 12th Century.
Factual error: They are present at Frankfurt, Germany. But with a closer look you see a cathedral at the right side. This cathedral and the central station are located in Cologne, Germany - they are about 220 km apart. (01:04:15)
Continuity mistake: In the final scene when Stark, Rhodes and the senator have a picture taken, Tony's jacket is first buttoned, then unbuttoned from the same viewing angle. (01:56:50)
Factual error: The type of book that Eli is protecting would actually be just a fragment. The complete Bible, in braille, occupies as many as 18 volumes.
Continuity mistake: Gamble and Hoitz get thrown to the ground when the accounting office explodes. In an overhead shot of them rolling around on the ground, Gamble's wooden gun has fallen from its holster and is lying on the ground. Cut to a side shot and the gun is back in its holster. Gamble had both hands covering his ears the whole time, he did not pick up the gun. Then comes another overhead shot, the wooden gun is again missing from the holster. (00:48:45)
Visible crew/equipment: If you look closely, after the shootings with the Russians and the guys go in to the second room, next to Chris Brown you can visibly see the camera man (shorts and the camera).
Continuity mistake: When the 3 guys are kicking a single guy with Kick-Ass defending him and a bunch of people behind watching the fight, the trashcan on the ground keeps changing positions between shots.
Continuity mistake: When the police car rolls out of the car wash, both passenger and driver's doors are open. When the shot changes to the deputy holding the rifle, the driver's door is closed. In the next shot both doors are open again.
Factual error: Outside Seville, Cruise jumps off a bridge on a stall with a sign that reads "Especial en sardines". This is senseless text. The correct spelling should be "Especialidad en sardinas".
Continuity mistake: When the karate kid first goes to Mr Han's house to train, he drops his jacket by the doorway. Later on as they are talking, you can see his jacket move to different spots on the ground between shots.
Factual error: Milo gets out of the car to pump gas, but they are in New Jersey where pumping your own gas is illegal.
Continuity mistake: When Royce kills the Predator at the end, he slices the head off, and it falls backwards, and the body falls forwards. One of the next shots now shows the head to now be in front of the Predator body.
Continuity mistake: When Machete is picked up by Booth in the S-class, the car changes from an S500 to an older generation S-class, and then switches back for the rest of the film. The footage was from the trailer being edited in.
Audio problem: When Scott fights Ramona's ex-girlfriend, Ramona holds his hands while punching her. One punch misses her but the sound of a punch is heard.
Continuity mistake: After the plane is docked Stallone and Statham enter the customs agency. Statham is wearing a camera on his neck with a small lens, he even shows it to the customs agent. After leaving the customs they walk across a square. The camera now has a big zoom lens attached to it. Statham is not wearing a lens bag. Where did he get that lens from? Also strange is that the lens is set in manual focus instead of automatic. Yet the picture stays focused even zooming in. This is not possible without looking at the screen. Plus the camera is turned off in the close up shot, with the image on the LCD composited in. (00:28:15 - 00:30:45)
Continuity mistake: Whenever Megamind or Minion uses the disguise generator, their normal eye colour always show through their disguises, such as when they both disguise themselves as the Warden (the Warden has blue/gray eyes while Megamind has green and Minion has brown). However, during the final battle, Minion disguises himself as Megamind but he has Megamind's green eyes instead of his normal brown eyes.
Suggested correction: Not necessarily. Some engines may not have a rear cab access (like Frank/Will's engine had). And even if the rescue engine did have a rear cab access 777's engine only had a side access stair which at the speed it was going is more difficult to climb over from the engine in front of it.
Actually 777's catwalk goes across the front, from side stair to side stair, but someone would have to leap over a rail or a chain to get onto it from the other engine. Why would there be stairs on the right side unless there was a catwalk to get to the door on the left side?