The broken fang on Half-Tooth switches positions when he menaces The Brothers and later as he drives the terror bird away from its kill.
During the introductory scene, in the closeup shot of Halftooth's animatronic head bellowing at the terror birds, there is a hairy piece of dirt on one of his teeth. In the next shot, which is computer-animated, his teeth are clean.
Phorusrhacos was already extinct several million years before the timeframe of this episode. (The bird featured in the episode is actually its relative, Titanis. But since it is constantly referred to as Phorosrhacos, even in the book, this is a legitimate error.)
The saber-tooth of the female Smilodon forcing the Macrauchenia to the ground sinks into the latter's back a couple of times.
In the opening scene, when the terror bird flips the Smilodon cub into the air, the underside of the cub's paws are completely flat.
During the fight scene at the beginning, as the two Smilodon rear up, Half-Tooth's face momentarily passes into the rear of the other Smilodon.
When the female Smilodon launch their attack, there are a few strands of grass in the foreground that the body of the Smilodon overlaps, even though she's supposed to be farther away.
Obvious wrinkle on the back of the Phorosrhacos' head reveal it's a puppet. The CGI version of the animal has a smooth neck.
The carapace of the Doedicurus visibly bends at the front when it's being menaced by the young Smilodons, but its carapace was fairly solid in reality and attached to the pelvis, so it wouldn't have moved together with its upper body.
After Half-tooth's finished drinking, we see through his reflection in the water that he walks off to the side of the screen. There is a miniature waterfall where the nearby stream flows into the river, however he doesn't pass through it, even though his feet should be visible. The shot makes it look like he just floated off without touching the ground.