Art has the supernatural power of granting some supernatural resilience to his victims
They consistently survive their wounds way longer than they should be able to; Dawn is still alive after being sawn in half way down to her heart, and the woman who he scalps and partially skins also stays alive and conscious under such terrible wounds. We could infer that aside from maiming and killing, Art involuntarily makes his victims more resilient so they can be terrified longer. Art has, at least, a microscopic amount of humanity left
Art never misses an opportunity to do the cruelest thing possible, except once: when he spares the homeless woman's "baby" (doll) after she desperately pleads with him.