Just read a forum on petopia that said the silkworms and porcupines that are part of the "boar" family weren't meant to be tameable pets, but they forgot to change that part when they got rid of the boar placeholder models.

Please don't take away my porcupine. He's as little as a hyjal bear cub and as ferocious as Garrosh with a hangover. Every time i see his little spiky body run out of a pack of giant dead mobs he's tanked for me, i smile.