Other mistake: Even though it is snowing throughout much of the movie, none of the snow seems to stick to any of the characters' fur. Even during the fight scene when they are rolling around in it, they are never covered with white.
Continuity mistake: When the squirrel gets stuck between the 2 glaciers he gets stuck at the bottom of them, but then it shows him getting fired out of the top of them.
Plot hole: In the Ice Tunnel scene, Manny, Sid, and Diego come to a stop on the vertical block of ice. It breaks, and they slide through a 'field' of icicles sticking out of the ground. Their 'sled' is shaved down to nothing, indicating that the icicles are sharp. After going through the same tunnel as the baby, how did the baby make it through that field?
Continuity mistake: The scene where Scrat is trampled you see the feet of a camel-like animal and the feet of a mammoth. When the camera pans up, the mammoth is nowhere to be seen.
Continuity mistake: Near the beginning of the movie, when Sid decides to return the baby, he starts trying to climb up the cliff. The baby falls out of the little sleeping bag. After that, we never see it until it's used in the plan to escape the saber-toothed tigers. Animals don't have pockets, and I don't remember seeing anyone carrying it around, so where was the sleeping bag in between these two times?
Continuity mistake: Scrat lands on the main road and is not stepped on for 16 seconds. During that time, not one animal passes by. Yet once he is stepped on, the animals pass by at 2 to 4 seconds each, and when the camera pulls back, you can see dozens of animals. Scrat should have been hit as soon as he landed.
Continuity mistake: When Lenny and Oscar witness Soto's death, they are standing next to each other. But, in the next shot where Manny looks at them, Oscar is standing further apart from Lenny. They stand next to each other in the next shot, but in the shot where they flee, they're standing apart from each other again.
Continuity mistake: At the beginning of the movie, the feet of two mammoths and a dodo bird can be crushing Scrat, but when the camera pulls away no mammoths or dodos can be seen in the herd.