You may have seen many stupid horror movies in which dead people were revived by supernatural or scientific ways, and the dead ones were very akin to the flesh of their living relatives.

These characters possess very limited intelligence and do or don't control themselves. And are named zombies.

But in fact, the zombie fiction originates in the Afro-Caribbean Vodoun (Voodoo) religion, where there are indeed dead-people brought back to life.

In Voodoo, a dead person can be reanimated by a bokor (black magician), which totally controls them as zombies have no will of their own (that's why in philosophy, the term "zombie" designs a person who lacks full consciousness but acts like normal people). Zombies have lost their souls (named "Ti Bon Ange" - French Caribbean Creole for "petit bon ange", or "little good angel") to the bokor. As they do not possess free will, they will be put to work as uncomplaining slaves for a "zombie master", mostly on plantations.

Europeans thought that, if such "zombies" existed indeed, they must have been heavily drugged but they still are living humans.

"Zombie" is also another name of the voodoo snake god Damballah Wedo, of West African roots; in some Bantu languages "nzambi" means "god."

The secretive nature of the Voodoo religion just increased the mystery about zombies.
Some zombie cases were signaled, but science could not rely on them. "What is more, if science ever gets to the bottom of Vodou in Haiti and Africa, it will be found that some important medical secrets, still unknown to medical science, give it its power, rather than gestures of ceremony", wrote in 1937 researcher Zora Neale Hurston, while in Haiti.

Only in 1980's, the Canadian ethnobotanist Wade Davis might have found the secrets behind the zombies. As a result of his investigations led in Haiti, Davis claimed that a living person can be turned into a zombie by two special powders injected into the blood stream (commonly via a wound). The first powder contains tetrodoxin (TTX), a powerful neurotoxin that induces a 'death-like' state.

Near-lethal doses (1mg) can leave a person in a state of near-death for several days, while the person continues to be conscious.

The toxin paralyzes all the bone muscles of the subject (which usually dies when the breathing muscle diaphragm stops). Tetrodoxin molecules are very potent and unbind from the nerves very slowly, that's why slight doses keep a person paralyzed for days. The toxin is produced by some bacteria, but is usually concentrated on their host: some fish species (especially porcupinefish, pufferfish, parrotfish), Atelopus toads from Central America, Taricha newts (from North America), seastars, some marine worms, crabs and tinny octopuses.

Most likely, voodoo priests get it from sea products.

As Japanese find pufferfish (fugu) a delicacy, this sushi must be prepared with care, in order to remove venomous skin and internal organs.

The second powder may contain hallucinogens like datura that introduces the person into a zombie-like state where they seem to have no will of their own.

Many are still skeptic about Davis's findings but there is wide acceptance among the Haitian people of the existence of the "zombi drug". As voodoo is very secretive in its practices and codes, it is almost impossible for a foreign scientist to validate or invalidate such claims.

Some psychiatrists linked it to social and cultural expectations - in the context of schizophrenia and other mental illness - suggesting that mental illnesses may explain some of the psychological aspects of zombification.