Plot hole: During the scene where Merida gives her speech on "breaking tradition", her mother, as a bear, moves silently behind the majority of the crowd, so they don't see her. Fair enough. However, Merida and her father's clan are all looking in the same general direction (towards the crowd) while she's speaking - how does no one from Merida's clan see a bear moving at the back of the room?
Revealing mistake: When Alex says they should go find the penguins, he says "To home" and Marty, Melman, Gloria and Julien place their hands on top of his hand. In the next shot it shows all of them together. But due to the position of Julien and his arm length, it would have been impossible for Julien to have his hand fully placed on Alex's hand. (00:05:05)
Factual error: Johnny shows Mavis the sunrise by keeping her back in the shadows. But if your whole body is in an object's shadow then you can't see the light source. The rising sun is reflected dead center in Mavis' eyes, which means the sunlight is touching her, which means she ought to be on fire.
Continuity mistake: When Dex is being interviewed in the park, he is holding the basket of baby kittens that he rescued. He is never shown handing the basket to anybody else, but just seconds later, as everyone leaves and Dan arrives in the scene, the basket of baby kittens has suddenly vanished. (00:04:30)
Revealing mistake: When Sparky's tail pops off there is a hole where it popped off. But when the tail goes into the bucket the hole is gone.
Factual error: The pirates' map shows a drawing of Tower Bridge, which Pirate Captain sees through the telescope moments later. Construction of Tower Bridge started in 1886, and it was completed in 1894. Queen Victoria was 73 when Tower Bridge was completed, whereas she is in her late twenties or mid thirties here. The sign setting the film in 1837 also makes no sense given this timeline. (00:25:20)