In addition to litter box snacking I've caught Devon several times chewing on the stones and mortar where the fireplace comes in contact with the floor. He's actually managed to tear off some chunks of the mortar between the stones! I've never heard of any dog, or even puppy, chewing on mortar and stone. I don't know how bad it is if he actually swallows some of the small mortar pieces, which worries me. I'm doing my best to keep him away from it, and hoping that he outgrows it soon.