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.
Other mistake: After Scrat's landing you can see three pair of feet who are stomping on him. At least two of the three pairs belong to tetrapod vertebrates (as can be seen when the camera pans up to behind the herd), so where is the second pair of their respective owner's feet? (00:03:10)
Other mistake: The scene where Manny builds his shelter, he is bothered by what Sid is saying and, after Sid asks him about his family, he turns around. The shelter that Manny has built is not large enough for him to turn around in it unless he walks out and turns around, which he does not do. (00:13:37)