BLOOD: The bloody knives, victims, and vampires featured in today's popular games, movies and Halloween parties show the timeless allure of gore and violence. The Celts, like other ancient cultures, believed that the gods that controlled the forces of nature craved blood sacrifices -- human or animal. This picture shows an Aztec priest lifting the heart he just cut from the chest of a living sacrifice. It could as well have been a Mayan priest or any other devotee of the cruel forces from the world of the occult.