Continuity mistake: In the scene where Grug is chasing after Guy, they both wind up stuck in a tar pit. After successfully escaping they are covered in tar and Grug even gets himself stuck to Guy. In the next scene everyone is running from the exploding ground up between the mountains and both Grug and Guy are completely clean and free of tar.
Continuity mistake: At one point, Grug gets bitten in the bum. It's clear that his undergarments are made from lion skin. Yet in the next shot where he's climbing down, his undergarments are now just plain gray.
Plot hole: When Grug is trying to escape from the explosion behind him he sees Douglas and says "Douglas! Hey I know that guy!" This is not possible since he neither knew the name of the creature or was nowhere around when Douglas was with Thunk.
Continuity mistake: During the Croods' journey to the mountain they travel through several different areas including a lake, yet in some shots the background to the mountain shows a clear, open field of nothing.
Continuity mistake: When Epe meets Guy, at the fire for the first time, she throws a big rock at him. He yells in pain, and you can see his leg is pinned. But as she picks him up and sniffs at him, the rock is two or three feet away. Even if the rock rolled off his leg, it was way to heavy to lift him up with no effort at all.
Continuity mistake: When Grug runs out of the cave in the beginning, he scares the dog-like creatures away. At first there are only six creatures. In the next shot, another one is added, in which Grug scares away last. (You can tell he's new because he's a different color than the rest).
Continuity mistake: Gran's excessive body hair completely disappears after we see it the first time.
Continuity mistake: The position of Grugg's family on the wall that he draws near the end of the movie changes when the camera reveals the full image. This is especially noticable when Granny is further away from Ugga.