Diego: (smirking) Yeah, and it's got a nice fur coat on it.
The script doesn't shy away from the darker reality of the era. The opening newsreel style narration and various conversations touch on the fact that many species are dying out. Manny is initially presented as the last of his kind. The dialogue carries a weight of melancholy—"I'm not going to be the last one." This adds stakes to Manny’s survival; he isn't just grumpy, he is grieving the loss of his species. ice age 1 transcript
Manny: (skeptically) Great. Just what I needed. A sloth. Diego: (smirking) Yeah, and it's got a nice fur coat on it