Haven't you read the manga where the girls hold in their shits and as a result their shits turn into some concrete-like substance and get stuck just inside their assholes and fill up all their insides? Then they take to hacking their sphincters with razor blades (and unravelling their intestines out, filled with rock-solid shit) or put little sticks of dynamite in-between their assholes and the tightly packed shit and blow most of their lower bodies off. Later a little girl with only stumps for limbs crawls over to her sister and tries to nibble all the hard shit out of her anus for her.