Polycephaly

[2] In humans, there are two forms of twinning that can lead to two heads being supported by a single torso.

In humans, as in other animals, partial twinning can result in formation of two heads supported by a single torso.

[8] Giacomo and Giovanni Battista Tocci (born between 1875 and 1877), were dicephalus parapagus dipus twins who survived to adulthood.

Abigail and Brittany Hensel, born in 1990, are another instance of dicephalus parapagus dipus twins who grew up.

Each twin has her own complete head, heart and spine, and controls one arm and one leg.

[10] Other species with known two-headed occurrences include cattle, sheep, pigs, cats, dogs, and fish.

"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.

[12][13] On October 31, 2006, the World Aquarium[14] announced that "We" was adopted by Nutra Pharma Corporation, a biotechnology company developing treatments using modified cobra venom and cobratoxin.

[15] "We" died of natural causes at age seven in June 2007, not long after being acquired by Nutra Pharma.

A live two-headed tortoise named Janus can be seen at the Natural History Museum in Geneva, Switzerland.

[17][18] In cases where multiple heads are fully developed and non-parasitic, they share control of the organs and limbs, though the specific structure of the connections varies.

A two-headed black rat snake with separate throats and stomachs survived for 20 years.

[22] In early Germany, conjoined twins that could not be separated were legally considered one person.

[23] Millie and Christine McKoy were often referred to in the singular, including by themselves, with the name "Millie-Christine",[24] as well as plural.

The February 22, 2007, issue of the journal Biology Letters detailed the discovery of a 122 million-year-old fossil of a two-headed Hyphalosaurus lingyuanensis, marking the earliest known occurrence of axial bifurcation.

Recent two-headed kittens include: Polycephalic cats in museums include: A full body taxidermy of a two-headed calf is on display at the Garth and Jerri Frehner Museum of Natural History on the Southern Utah University campus in Cedar City, Utah.

This calf, or calves, joined from the beginning of the neck as far as the belly, with two complete, almost perfect body frames, had but one system of vital organs.

Dr. A. C. Johnson, of Cedar City, Utah, stated that this was the best specimen of monstrosity in animal life that he has ever seen or heard of in his 47 years of practice as a veterinarian.

"The Dancing Calves" were owned by West and Gail Seegmiller who displayed them for many years at their Desert Pearl Cafe (no longer in existence), in Cedar City, Utah.

Their offspring, by one source or another, account for many of the major monsters of Greek mythos, including: Other multi-headed creatures in Greek mythology include: Zahhak, an evil figure in Iranian mythology - also evident in ancient Iranian folklore as Aži Dahāka (Azh dahak) - is the most significant and long-lasting of the ažis of the Avesta, the earliest religious texts of Zoroastrianism.

The divine white elephant Airavata is depicted with multiple heads, trunks and tusks.

Judah was initially dismissive, but then another man came in saying that his wife had just given birth to a two headed baby, and asked a (different) halachic question.