I've had my russian tortoise, Sheldon, for about a week and I've noticed that he has trouble biting his food as though his bite is not strong. He has to bite a few times to break the leaves. I've tortoise sitted for my cousin's russian tortoise before I got mine and hers always chomped with no problem devouring greens. I did get him from a pet store so I am not sure what he was previously fed. When I first fed him it was a mix of romaine, green lettuce, and swiss chard. he sniffed at it for a bit before deciding it was edible and ate it all. I've tried googling answers with no luck.
