Polycephaly is the condition of having more than one head. The term is derived from the Greek . The most commonly observed two-headed animals are turtles and snakes. Other species with known two-headed occurrences include cattle.
Scientists have named a rare two-headed snake Double Dave after it was found in a forest in the US state of New Jersey. The baby timber rattlesnake was discovered last month by environmentalists from the Herpetological Associates group, who study endangered and threatened reptiles.
The reptile would have been easy prey for predators, environmentalists say.
The two-headed monsters of myth may have a basis in reality. Two-headed snakes are rare but not unheard of, and one recently found in Spain.
Vets say the boa constrictor is a Siamese twin contained in one outer skin.