Revealing mistake: When the main characters enter the underworld, there is a shot of them walking past a burning fountain. If you look closely at the shadows of the characters, they don't correspond with the lighting coming off the fountain.
Revealing mistake: After the prince is crowned king, Robin and his mates leave the castle. If you look to the upper-right of the screen, atop a hill in the distance, you can see a modern-day metal telegraph tower (cinematic version).
Revealing mistake: In the beginning scene when the dragons are attacking Berk, it shows several sky torch things being raised into the air. As one closest to the camera is rising, a Viking throws a burning stick at it to ignite it. If you watch it closely, you can see the torch starts burning first to the far left, well out of reach of the thrown fire. Even allowing for fumes igniting, the fumes nearest the flame should light first.
Revealing mistake: In a close-up, just after the defeat of the Jabberwocky, the White Queen collects the Jabberwocky's blood dripping from its teeth into a vial. Cut to a wider shot with the vial just over half full, you can see that the drips are still being caught by the vial (ie, they don't drop past it onto the ground), but the level of blood in the vial doesn't rise, revealing that it is done in post-production.
Revealing mistake: Eustace, in dragon form, is flapping his wings with all his might as he tows the ship. But in the overhead shot, while he continues flapping, his shadow on the water below is completely motionless.
Revealing mistake: During the scene where Kirk has an "accident" in his pants, the dog goes over to lick the stain. During this seen you can easily notice some sort of beef on the stain, probably to make the dog lick it.
Revealing mistake: The guns that the soldiers use to kill piranhas with are actually Nerf Longshots that you can buy at the toy store.
Revealing mistake: During the shower scene with Ally, part of Tyler's scratches disappear, due to it being makeup that was washed off in the water.
Revealing mistake: When Salt sits on the helicopter there are two of the same cuts with Salt looking through the heli's window with yawning guy in the background. Cuts split by the view of Washington DC.
Revealing mistake: During the scene where Jennifer Lopez does not have her body pillow, she has to use her friend/neighbor as a pillow so she can sleep. The nightshirt Jennifer is wearing allows you to see the fake pregnancy belly she has on.
Revealing mistake: Despite receiving several shots and crashing against other boats, Elise's wooden boat structure remains undamaged.
Revealing mistake: When Dominic West is captured and chained in the Pict village, you can see a hearing device in his ear. (00:38:55 - 00:41:35)
Revealing mistake: Throughout the movie, people getting shot almost always don't have the shot angles line up with how they appear. This is especially obvious in the end scene with Hit Girl shooting the gangsters: she might shoot someone at an angle from the side, but the shot appears to have come from directly behind the person.
Revealing mistake: When Mike shoots the cop in the beginning you see him fall on a mat to cushion his fall.
Revealing mistake: In the final scene we see a bomb disposal technician disarming a nuclear bomb. The screen of the laptop is shown in one brief shot. It displays a database program of some sort, and has been filled in, perhaps to look like it contains lots of helpful, bomb disarming related information. However, it is actually just random button mashing; most of the 'codes' consist of the letters 'dfgty'. Look at where they are on the keyboard. Very lazy: dgght dfhdftyh fghrthy.
Revealing mistake: In the scene where Rachel McAdams goes to Patrick Wilson's office to explain why she left the bar so abruptly the night before, there are four TV monitors behind her as she does those weird charade movements. Only one monitor has a picture. The picture is of the New Jersey anchors of the job from which she was previously fired. Also, the characters in the picture never move.
Revealing mistake: Throughout the phonecall between Killer and Lucy, the call duration on the iPhone stays the same at 00:03. (00:37:00)
Revealing mistake: Horvath is trapped in the bathroom mirror, and after knocking on the mirror from the inside, a boy comes over. You can see that the shadow from the boy's shoulder is falling on Horvath, and when he turns and falls over, if you watch closely, you can see that the boy bumps into Horvath's arm. This is because the boy actor is standing in front of Horvath's actor to achieve the mirror effect.
Revealing mistake: On Gulliver's MacBook when he is plagiarizing , he has the wrong program active at the top (Finder for Macists), when he is typing on the keyboard. He also doesn't have a single word-processing application open, which can be viewed at the bottom.
Revealing mistake: Throughout the film the actors' breath is visible. This wouldn't be happening during the summer when the film is set.