An amphisbaena is a mythological two headed-snake. While real two-headed snakes exists, they have two heads on the same side, while the amphisbaena has a head on each end. The word amphisbaena is derived from the Greek word for "to go both ways."
The amphisbaena first appeared in Greek mythology, which held that it was born from the blood that dripped from Medusa's severed head. It is said to be poisonous and to feed on ants and corpses. Later, the amphisbaena became a part of cultural lore throughout Europe.
In the Middle Ages, depictions of the amphisbaena, like those of many mythological beasts, were varied. Sometimes, it was a winged serpent, and in other depictions, it was hardly a serpent at all. The medieval amphisbaena could have legs, horns, ears, and a smaller "rear head" growing in place of a tail.
Like a real two-headed snake, the amphisbaena has separate brains in each of its heads. In some tellings, it can separate into two creatures, while in nearly all descriptions, it can travel in either direction. The snake-like amphisbaena can also take one head in the mouth of the other and roll in a hoop, like the mythological hoop snake of North America.
Though the amphisbaena is poisonous, it had some uses in medieval folk magic and medicine. Wearing a live amphisbaena around the neck was said to promote safe pregnancy, perhaps suggestive of just how dangerous pregnancy was in those days. The skin of an amphisbaena was said to help with arthritis or a cold. Killing an amphisbaena or eating its flesh were powerful forms of magic, allowing the practitioner to become pure of heart or to attract a lover.
A real animal that takes its name from the amphisbaena, the amphisbaenia, is a "worm lizard" native to South America and parts of Africa, the Middle East, and Mediterranean Europe. Novelist T. H. White suggested that this creature may have inspired the mythical amphisbaena. The amphisbaenia is similar in color and appearance to a worm, but is actually a relative of lizards and snakes. Like its mythical cousin, the amphisbaenia can slither equally well in either direction, and its head and tail are difficult to distinguish at a glance.