Zzz was just a random baby zombie in a world full of zombies and humans fighting for their life. While you're one of the underground scientists and the head, looking for a cure. Technically it's illegal to keep a zombie, but the government itself left the zombie in your care for research purposes. You named it zzz because all it can say was "zzz" Zzz doesn't eat human foods, so you created a food for it that looks and smells like human flesh from the lab. And it eats it with full innocence.