The undead are generally known as brain-eating monsters, but they haven’t always been that way

In 1981, a man wandered through a busy marketplace in l’Estere, a small village in central Haiti. He spotted a peasant woman, Angelina Narcisse, and weaved through the crowd towards her. Introducing himself as her brother, Clairvius Narcisse, he spoke of details from their childhood that no stranger could know. Angelina stared at him in disbelief.

She had reason to be suspicious. Clairvius had died eighteen years ago.

Clairvius’s story is one of the best documented cases of Haitian zombies. While some may dismiss zombies as movie myth, most Haitians believe they are real. Up to a thousand cases of zombification surface each year. However, unlike the human-hungry, blood-lusting monsters of Hollywood, Haitian zombies are pitied, not feared.

Many Haitians in rural areas practice Vodou, a West African religion involving spirits and sorcery. They believe a Vodou sorcerer, or boku, creates zombies to exact revenge on another Haitian or acquire slave labour. The boku strips a victim’s spiritual essence, called the ti-bon anj, from the physical body. The body, now deprived of free will, becomes the boku’s slave.

But are the stories of Haitian zombies simply folklore? Could reports of zombified relatives and friends be cases of mistaken identity, or possibly mental illness? In a country where deaths are recognized by locals but not doctors, where bodies are often buried within a day or less, and where mental illnesses go undiagnosed, the zombie mystery could have an easy answer.

While some may have accepted these easy explanations, the possibility of the deceased coming back to life has intrigued members of the scientific community. One interested scientist was Canadian Wade Davis, a Harvard PhD candidate. While Davis did not believe in the zombie folklore, he did suspect the existence of a “zombie potion.” This concoction would dramatically lower a victim’s heart rate and respiration, apparently killing them, but allowing them to recover after a few days.

Davis’s search for the potion began in 1982, when he arrived in Saint Marc, Haiti and contacted a boku named Marcel Pierre. Pierre confirmed the existence of the potion and agreed to show Davis how to make it for $300 per vial.

Pierre ground parts of toads, sea worms, lizards, tarantulas, puffer fish, and human bone (which he and Davis acquired by digging up an infant’s grave) to make the black, dirt-like poison. The powder is rubbed into the victim’s skin and quickly causes perspiration, induces nausea, and impedes breathing. The victim feels a prickling sensation throughout their body, similar to a limb falling asleep. The prickling progresses to full paralysis and the victim’s breathing becomes so shallow that their lips turn blue from lack of oxygen. In as short a span as six hours, the victim’s heart rate and respiration become so faint and slow that they appear dead. Most of the time, the victim suffocates, but in rare cases, they can fully recover and seemingly “rise from the dead.”

Davis identified the puffer fish as the key ingredient in the zombie potion. Puffer fish carry tetrodotoxin, one of the most powerful poisons known to man. Many documented cases of puffer fish poisoning exist, especially in Japan where a species of puffer fish known as fugu is enjoyed as a delicacy. Japanese chefs remove just enough poison to make the dish non-lethal while giving diners a tingling sensation along the spine. Although these chefs require special training and licensing, about 100 Japanese die each year from improperly prepared fugu.

Tetrodotoxin blocks the sodium channels in myocytes, the cells that contract muscles. When the myocytes cannot function, the victim becomes paralyzed and suffocates as their diaphragm stops contracting. At near lethal doses, the poison slows metabolic rate. The victim remains conscious, but unable to move or speak. If the victim survives the initial paralysis they will likely recover once the poison wears off. A Japanese man who “died” after eating fugu-fish woke up in a morgue seven days later.

The tetrodotoxin theory only explains half of the zombie mystery, though. Once the victims recover, the boku must be able to control them. As Davis notes, “Japanese victims of puffer-fish poisoning don’t become zombies, they become poison victims.” While the tetrodoxin explains how a dead victim can come back to life, it doesn’t explain why they turn into a mindless slave.

Davis believes the boku uses a second ingredient, known in Haiti as concombre zombi or the “zombie’s cucumber,” to disorient their revived victim. Concombre zombi is part of the Datura family, plants with spiny green leaves and a thick woody stock. When ingested, these plants cause delirium and, in high doses, amnesia.

While Davis’s hypothesis seems plausible, he hasn’t yet convinced the scientific community. Kao Yasumoto of Tohoku University in Japan analyzed Davis’s zombie powder for tetrodotoxin in 1984 and found “insignificant traces.” Kao also adds that the likelihood of victims reviving after poisoning is insignificant.

Davis defends his theory, citing variable powder content as the reason for Kao’s low tetrodotoxin reading. Powders carry varying amounts of poison, since ingredient measurements are imprecise and poison levels in puffer fish depend on their species, gender, and the time of year. He argues Kao’s lab analyzed a less concentrated sample of the powder.

As for the odds of a Haitian falling victim to a perfect, near-lethal amount of tetrodotoxin, Davis agrees that it must be a rare occurrence. “I’ve never maintained there is some kind of assembly line producing zombies in Haiti,” says Davis. “I’m not even saying it’s happening today.”

He also notes that if the boku uses too much poison, the victim simply dies. Too little, and the victim falls ill but recovers. In either case, no one knows of the boku’s failure.

Critics will continue to argue that Davis’s research proves nothing, and that he failed to find the smoking gun—an actual zombie. But this was never his goal. “How many zombies there are is not the question,” he explains. “It doesn’t really matter as long as it’s a possibility.”