I house 4 star torts in one same closure. Recently, I notice that one of the smaller tort, about 3 inches, biting of the side of the shell and forelimbs of a bigger star, which is about 4 and 1/2 inches. the smaller tort also try to stick its head into the shell of the bigger tort when its head goes in to hide and seem to bit it. They have not show any of these sign before and i could not tell them apart from male or female as they are still so small. Are they playing or mating ? Is this normal behaviour ?