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.
Revealing mistake: When Leo is laying his dead kids on the grass, the little girl keeps moving her eyes and breathing.
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: When Mark types email addresses in to tell people about facemash, he writes to several people @harvard.edu. At the time the movie takes place, undergraduate email addresses were all of the form username@fas.harvard.edu. Furthermore, the network brought down by facemash would have been referred to as the FAS network. (FAS stands for Faculty of Arts and Sciences; the eponymous network covered all buildings within the College and Graduate School of Arts and Sciences.).
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: John's staff sergeant military shoulder epaulet markings become upside down in the scene when he and Savannah are having dinner at her house when he comes to see her after his dad died. In a later shot shortly after, they are correct.
Other mistake: When Elizabeth (and later Elizabeth and Bertie) visit Lionel's flat, they take the elevator down. With its huge windows, the flat is obviously not below ground level. And certainly no one would ascend to a higher floor only to take the elevator down to his destination.
Visible crew/equipment: Near the end of the boat chase, after the railing and Frank are pulled into the water but prior to the cut to Elise slowing her boat to allow Frank to board, a member of the crew can be seen exiting the cabin of Elise's boat. (00:05:50)
Factual error: The day Carrie arrives in NY: June 11, 1986 was a Wednesday not a Tuesday.
Plot hole: When Astrid gets on Toothless for the first time, Toothless takes off uncontrollably and tries to scare her. Hiccup seems to have no control over him at this time. How is that so if with the new tail fin, Toothless cannot fly without Hiccup's precise control of the tail fin? That whole sequence would have fallen apart. This mistake was even admitted to on the DVD commentary. (00:53:35)
Continuity mistake: In the scene where Sophie is first walking out of the New Yorker building, her shirt is tucked in in the first shot, in the second it is untucked, and in the third it is tucked in again.
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.
Continuity mistake: When Ray Winstone takes his pill with whiskey while talking to Mel Gibson, he takes a swig of the drink and knocks the pill back, leaving some alcohol in the glass. When we cut to a wide shot his glass is completely empty.
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.
Visible crew/equipment: Several times during the movie, when Jacob rides his motorcycle you can see the camera reflection in his helmet.
Plot hole: When Claire is getting interviewed at the FBI building, there's pics of inside the bank during the robbery, even though the security tapes were destroyed in the microwave.
Continuity mistake: In the final dance Julien is wearing the samurai jacket, but when the camera changes angles and then focuses back he isn't wearing the jacket. This happens at least three times.
Continuity mistake: When Will has come to apologize and talk to Ronnie after she has left the volleyball game practice, Ronnie's father opens the door to a sweaty suitor. The door is closed and when it is reopened just a brief moment later, Will is no longer sweaty.
Factual error: When Ewan McGregor drives to Belmont MA to visit Paul Emmett, he checks the mailbox to see whose mail it's addressed to. It shows the name Paul Emmett, address, Belmont MA 02324, which is the wrong zip code; it is the zipcode for Bridgewater MA, and Belmont MA should be 02478.
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?