Suffer the Children by John Saul. At one point a 13 year old girl kills a cat with a rock and dresses it in doll clothes, then she has a tea party with it in a mineshaft and ends up swearing at it because the corpse won't respond and then beating it and finally cutting it's head off with a butcher knife in a mad rage. It made me really sad to see her abuse the animal so horribly.