Revealing mistakes: During the scene where we see Memphis and Norma Jean finding each other in the crowd (when the females are returning), one penguin in the center of the screen walks through another penguin.
Continuity: While Baby Mumble is with the Skuas, a small black bow can be seen on Mumble's chest. However, when Mumble falls into the crack in the ice, the bow disappears. When the birds fly away, Mumble rolls to the side and begins to cry, with his bow visible again.
Continuity: Toward the end of the movie, the penguins start to dance while one human video tapes them. Later, the video of the penguins dancing is played in Times Square and on TVs all over, but the human didn't even have his camera out yet during the beginning part of the dance that is televised.
Miscellaneous: When the Adelies and Lovelace are involved in the killer whale attack on the frozen buoy, Mumble surfaces. When he starts speeding up, there's no wake seen behind him..
Factual errors: When Mumble is in the aquarium, there is a long zoom out until the earth is visible as a small disk in space. Stars in the background twinkle. However, stars should not twinkle when seen from space. They only twinkle when seen from earth because of variations of the atmosphere.
Revealing mistakes: When Mumble and the Amigoes are outrunning the avalanche, Mumble hangs in mid-air for a few seconds, and Ramone grabs onto Mumble from behind before they fall. Looking closely, you can clearly see that Ramone's flipper passes through Mumble's feathers right before they nose-dive down the slope.
Audio/visual unsynchronized: In the scene where Mumble is born, Memphis says "woah" a little bit before Mumble's foot actually comes out of the egg.