You would be forgiven in this age of deep fakes for wondering whether you can believe what you see when it comes to reports about two-headed snakes and other animals.
But this eye-catching developmental abnormality — known as bicephaly or dicephaly— is a phenomenon that has been around for at least 150 million years.
And over the years there have been reliable reports of a veritable menagerie of two-headed creatures, including snakes, bulls, sharks, turtles and prawns — and then there are two-faced kittens.
So how common are two-headed animals and what causes them?
Among the most common reports are two-headed snakes, yet these are certainly still rare enough to surprise us.
Take the two-headed eastern copperhead snake discovered recently in a flower bed outside the front door of a home in Woodbridge, Virginia.
State herpetologist John Kleopfer, who collected the snake, said he was familiar with two-headed snakes resulting from inbreeding in captivity, but was "dumbfounded" by the discovery of one in the wild.
Without special care, such animals usually die early because they have difficulty escaping predators and foraging for food, Dr Kleopfer, from the Virginia Department of Game and Inland Fisheries, said.
Indeed, while the copperhead — which has a single stomach — is now feeding well, its two heads don't always co-operate.
"Sometimes with two-headed animals you'll get one head that's a little bit more dominant over the other one," Dr Kleopfer said.
"Sometimes the heads go in different directions"
An even more unusual two-headed snake was studied by Gordon Burghardt of the University of Tennessee some years ago. In his decades of studying of animal behaviour, Dr Burghardt has encountered four two-headed snakes.
This two-headed black rat snake had two separate stomachs — and its two heads fought over prey.
But it managed to survive for 20 years.
In more recent years, a two-headed yellow anaconda snake with two hearts, three lungs, two livers, and two stomachs was discovered in Brazil.
Over the centuries, hundreds of two-headed snakes have been reported, and it is worth asking why they seem to be more common than two-headed mammals.
We may well have a deep-seated fear handed down over the years of anything that sounds like a multi-headed serpent, and so take more notice of these creatures.
But might there also be a biological explanation for the observations?
According to Justin Adams of Monash University, who studies anatomy across the animal kingdom, including humans, there is.
Reptiles more likely than mammals to have two heads
Two heads can result from the incomplete splitting of an embryo (also called axial bifurcation), Dr Adams explained.
This process leads to conjoined twins in humans, although only a very small number of conjoined twins have two heads and one body.
It is also possible for two separated embryos to incompletely fuse to form a two-headed animal.
Two-headedness results from factors that cause malformation of a developing embryo, which can be both genetic or environmental. But it does not tend to be inherited, since two-headed animals do not usually live long or reproduce.
In mammals, "fact-checking" by the mother's body also tends to prevent the implantation of embryos that carry errors like this, Dr Adams said.
"If there are errors in development, there are miscarriages and spontaneous abortions," he said.
Dr Adams said animals with irregularities like two-headedness were likely to be conceived at a much higher frequency than we realised — with far fewer surviving long enough to be born.
He said there were two reasons why reptiles would be more likely to have two-headed offspring than mammals.
First, they have many more offspring: "So, it's a numbers game."
Second, reptile eggs are exposed to the environment, which means they can be more easily exposed to more factors that can affect the developing embryo.
"Things like temperature, radiation, chemical toxicity," Dr Adams said.
In addition, snakes are often bred in captivity, where inbreeding increases the chance of irregularities, and individuals with them are given support to survive.
Controversy over cause of two-headed fish larvae
Dr Adams said there was "no way of knowing" how frequently the phenomenon occurred naturally in the wild.
And this is one of the challenges in determining whether occurrences of two-headed organisms are due to anything other than random chance.
However, in one famous Australian case, some experts presented evidence that pesticide pollution from a nearby farm was the cause of a mass spawning of two-headed fish larvae in a hatchery in Noosa.
This theory was eventually rejected by authorities, although controversy over the cause of the incident continues.
Two-faced 'Janus' cats
Animals with two faces are an even rarer phenomenon involving duplication.
You may have seen photos or videos of Janus cats — named after the ancient Roman god with two faces — on the internet.
Some scientists say the condition, known as diprospus, is a variant of the change in embryonic development that leads to two-headed animals.
Others argue it is due to an increase in expression of the sonic hedgehog (SHH) gene, that is involved in development of the face and skull.
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Janus cats inspire human interest, although for quite different reasons to the two-headed snakes.
The short-lived South African-born kitten Bettie Bee was a recent Janus cat that captured the hearts of tens of thousands of people via Facebook.
So what about humans?
Most conjoined twins have separate bodies that are joined to varying degrees.
But there are a relatively small number of conjoined twins with one body and two heads. The most famous are Americans Abby and Brittany Hensel, who are now 28 years old.
It is estimated that one in 50,000 to 100,000 pregnancies may involve conjoined twins, but 60 per cent are stillborn or die shortly after birth, so they make up only around one in 200,000 live births.
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