My Toby would refuse to eat clams, snails, hermits, or any other kind of crab. He still would eat krill but turned his nose up at table shrimp. He chewed on my rocks every now and then and when he was done his teeth were nice and short. No big deal at all unless you don't like what he is doing to the rock. I had one puffer that even refused to chew on rocks so I had to handle him and trim his teeth with nail clippers. Only had to do it a few times. That was way back in the day when I kept freshwater Puffers and I realize now that the environment he was in was just too stressful for him.