of Norse mythology, Indra vs. Vritra of Indian mythology, Ra vs. Apep of Egyptian mythology, Yahweh vs. Leviathan of Judeo-Christian mythology, and Yu the Great vs. Xiangliu. Many other examples exist worldwide. Ouroboros Originating in ancient Egyptian iconography, the Ouroboros or uroborus is an ancient symbol depicting a serpent or dragon eating its own tail. The Ouroboros entered western tradition via Greek magical tradition. In Norse mythology, the Ouroboros appears as the serpent Jörmungandr, one of the three children of Loki and Angrboda, which grew so large that it could encircle the world and grasp its tail in its teeth. In the Aitareya Brahmana, a Vedic text of the early 1st millennium BCE, the nature of the Vedic rituals is compared to "a snake biting its own tail." It is a common belief among indigenous people of the tropical lowlands of South America that waters at the edge of the world-disc are encircled by a snake, often an anaconda, biting its own tail. Founding myths Many cultures have myths describing the origin of their customs, rituals, and identity. In fact, ancient and traditional societies have often justified their customs by claiming that their gods or mythical heroes established those customs. For example, according to the myths of the Australian Karajarri, the mythical Bagadjimbiri brothers established all of the Karadjeri's customs, including the position in which they stand while urinating. In the Old Testament, the Israelites have a founding myth of their ancestors escaping enslavement from Egypt. Structure of hero narratives Folklorists such as Antti Aarne (Aarne-Thompson classification systems), Joseph Campbell (monomyth) and Georges Polti (The Thirty-Six Dramatic Situations) have created structured reference systems to identify connections between myths from different cultures and regions. Some comparative mythologists look for similarities only among hero stories within a specific geographical or ethnic range. For example, the Austrian scholar Johann Georg von Hahn tried to identify a common structure underlying Aryan hero stories. Human cannibalism Human cannibalism features in the myths, folklore, and legends of many cultures and is most often attributed to evil characters or as extreme retribution for some wrongdoing. Examples include Lamia of Greek mythology, a woman who became a child-eating monster after her children were destroyed by Hera, upon learning of her husband Zeus' trysts. In Zuni mythology and religion, Átahsaia is a giant cannibalistic demon, feeding on fellow demons and humans alike. He is depicted as having unblinking bulging