Revealing mistake: When Flynn and Maximus are fighting to get the satchel, it flies off and gets snagged on a tree branch. But you can see it goes through the branch, and not around it.
Suggested correction: If you look closely, it is very clear that it doesn't go through the branch at all, but hangs from the side as it should.
Revealing mistake: During a large battle scene between the Fire Nation and the Northern Water Tribe, the camera pans to reveal a Fire Nation soldier fighting with no one.
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: 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: 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: Throughout the film the actors' breath is visible. This wouldn't be happening during the summer when the film is set.
Revealing mistake: The handheld device that Bob uses to adjust the satellite antennae is actually a very common label maker and printer sold in most Walmart stores.
Revealing mistake: When we see the man in the green shirt breakdancing, we can obviously tell that he is a professional breakdancer and not the same guy as the one breakdancing. The professional breakdancer is much thinner and reveals his face, which is completely different from the original man in the green shirt. (04:32:33 - 04:34:23)