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.
Continuity mistake: When Eduardo finds the letter on the mantlepiece about them apparently stealing the idea for Facebook and asks Mark if they did or not, he places a bottle on the mantlepiece just before he finds the letter. This bottle rotates slightly between shots without him touching it after placing it down. (00:49:15)THGhost
Continuity mistake: After the double train fails to slow train 777 and gets switched to another section of track, in the control room, you see the train has already partly gone around a bend on the TV screen behind the bearded character, then cuts to the TV report footage which shows the train continuing on for a few seconds, though when the scene cuts back to the train, it is only just beginning go around the same bend that it had already partly travelled. (00:45:20)Zentron
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.ABernacchio
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)Quantom X
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: On the inspector's boat Frank's wrists are handcuffed together with a railing between his arms to secure him in place. There is a very short chain between the cuffs, 4 to 5 inches at most. When he's pulled free by a rope from Elise's boat he starts 'climbing' the rope hand over hand. In one shot his hands are over a foot apart, he's obviously not wearing the handcuffs. When he gets onto Elise's boat his hands are cuffed once again, she shows him how to pick the locks to get the cuffs off.BocaDavie
Visible crew/equipment: Several times during the movie, when Jacob rides his motorcycle you can see the camera reflection in his helmet.
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.
Continuity mistake: When Elizabeth meets Lionel for the first time, her face netting disappears and reappears between shots.
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.