Kyon grabs pellets like he's never been fed before! Never heard him crunch though! He will headbutt the glass occasionally. My mums goldfish tantrums full on when she gets new fish! He picks up the gravel in his mouth and spits it at the glass like a toddler throwing his toys!
I've been bitten by Ky 5 times and it never hurt so I assume their teeth are very very small!
My first veiltail did would bang his jaw into the side of the glass. Never could figure out why. I had him on my desk at work and every once in a while i would hear it. Sounded like hitting the bowl with a pen or something.