Quote Originally Posted by Edea View Post
This right here sums it up. The bonus HD advancement for animal companions as their druid gains class levels is not the same as gaining class levels themselves; those are just basic d8 animal hit dice.
Sure, sure. But they still gain bonuses to Saves (Good Fort/Ref, Poor Will), BAB As a druid with the same HD, and Feats. So it's, for all intents and purposes, the same as leveling up.

I kinda have to play Asmodeus's advocate here, as my player isn't present...