Two-headed snakes do exist, but they are rare. These snakes are actually conjoined twins, or sometimes, a fully formed individual with a parasitic twin that only consists of a head. Though they are a rarity, they are more common than other animals with two heads and are sometimes on display at zoos or in traveling animal side shows. Some museums have preserved specimens of two-headed snakes.
Snakes with two heads do not have a long life expectancy, particularly in the wild. Each head has a brain and, usually, some control over the shared body, and the two cannot communicate with each other. Movement is therefore difficult, as each head may try to travel in a different direction, and in the worst case scenario, the heads may fight or try to eat each other.
Some two-headed snakes share a stomach, while others have a stomach for each head. In one with separate stomachs, one of the heads may die if it routinely loses fights over food. Even if there is only one stomach, the snake may not be able to capture prey if the heads are competing for food.
Despite these difficulties, some two-headed snakes have been known to live up to 20 years in captivity. Thelma and Louise, a two-headed snake that lived at the San Diego Zoo in California, had 15 offspring during her lifetime. Researchers have theorized that the inbreeding of snakes for zoos and pets may lead to an increased incidence of snakes with two heads, but this is very difficult, if not impossible, to verify, as it would entail getting an idea of how often these snakes are born in the wild. The fact that they would not live very long makes the task even more daunting.
In 2000, a two-headed snake named We earned a bid of $150,000 US dollars (USD) on eBay, but the site's policy against the auction of live animals prevented the sale. Instead, Nutra Pharma Corporation adopted the snake in 2006 to aid in their study of the pharmacological benefits of snake venom.