Craniopagus parasiticus
Craniopagus parasiticus is an extremely rare condition in which the two heads are joined directly together, and one twin (known as the autosite) has a functioning torso, while the other (known as the parasite) has only a vestigial torso. The parasite is supported by blood supplied from the autosite head. This threatens the life of the autosite by placing an additional burden on the autosites vital organs. Operations to separate the two heads have been performed in the hope of saving the autosite. Occurrence in animals
Polycephalic animals often make local news headlines when found. The most commonly observed two-headed animals are turtles and snakes. Other species with known two-headed occurrences include cattle, sheep, pigs, cats, dogs, and fish. In 1894, a two-headed partridge was reported in Boston, Massachusetts. It was notable as a dicephalic animal for surviving into adulthood with two perfect heads. Scientists have published in modern journals about dissecting such animals since at least the 1930s. A 1929 paper studied the anatomy of a two-headed kitten.Polycephalic animals, due to their rarity, are a subject of novelty. "We", a two-headed albino rat snake born in captivity in 2000 with both female and male genitalia, was scheduled to be auctioned on eBay with an expected price tag of $150,000 (£87,000), though their policy of not trading in live animals prevented the sale. On October 31, 2006, the World Aquarium announced that "We" was adopted by Nutra Pharma Corporation, a biotechnology company developing treatments using modified cobra venom and cobratoxin.
The demon-king Ravana Ravana is depicted and described as having ten heads, although sometimes he is shown with only nine heads because he has sacrificed a head to convince Shiva. Trishira his son is depicted with three heads. Animal races in Hindu mythology like Nāgas (serpents) may have multiple heads. The Naga Shesha is depicted with five or seven hoods, but said to have infinite hoods. Uchchaihshravas is a celestial seven-headed horse. The divine white elephant Airavata is depicted with multiple heads, trunks and tusks.