The legend of a howling man who shape-shifts by the light of the full moon strikes a particular chord come Halloween, as do the sunken eyes of flesh-hungry zombies that populate contemporary horror fiction. Both of these creatures stem from a long line of folklore, but like most myths, these stories are rooted in some degree of truth.

For centuries, civilizations have used legend to provide an explanation for phenomena for which they otherwise have no rational explanation. Today, scientists have tried to provide clinical explanation for these so-called mythological creatures that would have prompted people to develop stories about them. Though we can only speculate, the science behind these monsters provides an interesting take on some of Halloween’s most popular creatures.

Werewolves

The werewolf is a mythological creature common in European folklore. Though the legend of werewolves differs between cultures, the main characteristics remain consistent. Usually, the werewolf is associated with a man who is metamorphosed—or shape-shifted—into a wolf-like form. The transformation is attributed to various sources, such as putting on a belt made of wolf skin, full moons, or witchcraft. Recently, the werewolf has seen a return to pop culture through the Harry Potter and Twilight series.

While the werewolf dominates myth, some scientists have speculated clinical disorders that may have contributed to the development of such folklore. One explanation is the rare condition known as “congenital hypertrichosis universalis.” According to a study conducted by Robert Suskin and Nancy B. Esterly in 1971, patients of this disease are born with excessive body hair that increases with age. By age two, the person’s face, trunk, and limbs are covered with long hair—a state that could have contributed to the development of the werewolf myth. However, while symptoms of the disease seem to resemble the mythological creature, its rarity—fewer than 100 cases are documented worldwide—suggests that this medical condition alone could not have contributed to the widespread myth of the werewolf.

In his novel The Werewolf Delusion Ian Woodward points to rabies as a more likely cause for werewolf myths.

Rabies is a viral disease that affects the central nervous system, ultimately resulting in disease of the brain, and death. It falls into the category of zoonotic diseases, meaning it can be transmitted from other species to humans. Some of the early-stage symptoms of the infection include violent movements and uncontrolled excitement.

According to Woodward, late-stage rabies and its accompanying dementia and aggression may have caused communities to associate victims of rabies infections with becoming “bestial.”

In many cases, the infected animals are exceptionally aggressive and may attack other animals without provocation. The Center for Disease Control and Prevention (CDC) states that transmission of the rabies virus is due to the spread of infected saliva of a host to an uninfected animal. This aggressive behaviour ultimately facilitates transmission of the virus to other hosts through bites.

Woodward speculates that if a person contracted rabies from a wolf bite, the people around them could have assumed that the wolf passed some of its animal qualities to the victim of the disease. Although this theory is only speculation, it helps to provide an explanation for how the myth of the werewolf arose in ancient cultures.

Zombies 

Zombies made their most recent appearance on screen this year with the release of Warm Bodies and World War Z, but the walking dead have long starred in West African voodoo and Haitian folklore.

Costas J. Efthimiou, a physicist at the University of Central Florida, describes the case of the alleged “zombified” Wilfrid Doricent in the magazine The Skeptical Inquirer. Doricent, an adolescent boy from a small village in Haiti, is known in myth for returning to life as a zombie. According to the story, Doricent experienced dramatic convulsions, swelling of the body, and eight days later appeared to have died. Yet a short period after he was buried, the villagers were shocked to see a person walking through the village in the exact likeness of Doricent. As legend goes, Doricent was incoherent and unable to speak—some might say he had returned from the dead.

Efthimiou speculates that this case of supernatural magic was actually a result of poisoning. Tetrodotoxin (TTX) is a highly potent neurotoxin that is found in several organisms, including a species of puffer fish that lives in the waters of Haiti. The toxin blocks sodium channels in nerve cell membranes, preventing normal transmission of signals between the brain and body. Consequently, symptoms of TTX poisoning include paralysis of voluntary muscles and loss of sensation. The liver of the puffer fish can be made into a powder, which Efthimiou concluded could have been used to poison Doricent.

Based on Efthimiou’s explanation, the effects of TTX paralysis mimicked a coma, which would have caused the villagers to assume Doricent’s death. If, however, the symptoms of the poisoning were to subside shortly after his burial, it is possible that his survival instincts kicked in and he was able to dig himself out of the grave. The oxygen deprivation caused by the live burial would have led to brain damage, providing an explanation for Doricent’s subsequent incoherency.

That being said, this theory is just one explanation behind the scientific reasoning of the legend of zombies. Until more scientific evidence can be provided, Efthimiou’s idea will remain, like the werewolf proposition, simply speculation.