Two Headed Snakes

A famous successful modern case is that of the human dicephalic twins Abigail and Brittany Hensel, born in 1990. The twins have two separate heads and faces, they each have their own individual brains, spinal cords, and hearts. Abby and Brittany however have three lungs, and share all the other organs. Each twin controls the limbs and body parts on her "side", and with coordination that allows them to walk, run, play piano, swim, drive and do anything else they wish.
• One or two animals?
It is difficult to draw the line between what is considered "one animal with two heads" or "two animals that share a body". With humans, dicephalic conjoined twins such as Abigail and Brittany Hensel are considered "twins", i.e., two individuals. This makes sense as there is a range of conjoinedness, and non-dicephalic conjoined twins may be barely-conjoined and separable by surgery, as was the case with Chang and Eng Bunker. Although the Hensel twins only have one pair of arms and legs total, each twin controls one side of the body's limbs. On the other hand, Syafitri, born 2006 in Indonesia, were given one name by their parents because they only had one heart. With other animals, polycephaly is usually described as "one animal with two heads". One of the heads, especially in three-headed animals, may be poorly developed and malformed, and not "participate" much.