Two-Headed and Two-Faced Animals.

Two-headed animals are said to exhibit "Polycephaly" This is typically cause not by genetic factors but as an extreme version of conjoined twins. That is a single fertilised egg divides in the uterous but does not completely separate into identical twin, and instead duplicates only some body parts. A two-faced animal with a single head can also be produced by diprosopus which caused a duplication of facial features. Most animals with these conditions have short lives but others can mature and live normal life spans.

In 2009 the Noosa River in Australia was the site of a mass die off of Bass spawn, many of whom were found to have developed two heads. It was speculated that the cause might be organophospate pesticides used on a nearby Macadamia farm. This was one of many incidents of illness and death amongst animals in an around the river, and definitive proof of the cause was never found.

There seem to be a particularly large number of examples of two-faced or two-headed calves.

In 1950 a two-headed calf was born and lived for 5 days. Its stuffed remains are in display in the Idaho History Museum.

In 2009 a two-headed calf was born in Belgium.

In 2007 "Blinky" (pictured right) was born in a dairy farm in the United States and had to be euthanized after its lungs function became impaired. This video from Associated Press suggests the calf was not very vigorous or healthy even prior to suffering the collapsed lung.

There are fewer examples of adult cows with similar conditions. Although the Whte Coty Amusement park did once have one as an exhibit (date unknown).

Full-grown cattle with this condition are much more rare. This example is provided with no details about place or time. It may have helped that one of the head was clearly dominant and continued to grow when the other did not.

A fossil has been found that seems to be a very young Choristodera with two heads (2006).

The Choristdera was a dinosaur that lived partly in the water and was broadly similar to a modern alligator.

A two-headed fossil of another similar species was found in the same year.

This lamb is reported to have been born in China in 2007.

A preserved specimen of a two-headed lamb can be seen at the Daughters of the Utah Pioneers Museum.

Perhaps the most famous two-faced cat is the adult name Frankenlouie who has appeared on many television shows including Animal Planet (date of birth unknown).

In a very disturbing series of experiments Vladimir Demikhov's grafted the head of one dog onto the body or another and maitained life in both for as long as several months (1954).

• [Hoax] Bill Durks (1913-1975) actually suffered from frontonasal dysplasia, where the two side of the face don't come together. But he posed as a man with two faces by the use of a fake third eye placed in the central position.