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HBO's "Game of Thrones" kicked it up a notch on this week's episode with an extended battle scene featuring thousands of zombies and their undead overlords.
These aren't zombies in the sense of, say, "The Walking Dead" or "The Night of the Living Dead." Dead villagers aren't transformed because they're infected by the bite of a zombie, but because blue-skinned ice ghouls known as White Walkers work their dark magic.
Nevertheless, the wights shown in the series (and described in George R.R. Martin's "Song of Ice and Fire" novels, on which the series is based) are part of an undead tradition that goes back to the zombies of Haitian and West African lore, as well as the vampires and ghouls of other cultures.
Related: Zombies Roam the Animal Kingdom
Do real-life zombies exist? That question is still under debate. In the 1980s, anthropologist Wade Davis put forth evidence that some Haitian voodoo priests used zombifying concoctions containing tetrodotoxin, a paralyzing poison extracted from pufferfish.
Davis claimed that the tetrodotoxin and other poisons put victims into a deathlike comatose state. After the seemingly dead victim was buried, he or she would be dug up by the zombie maker's assistants and drugged into undead subservience.
Over the years, some researchers have cast deep doubts over such claims. In their view, it's more likely that the voodoo victims fell prey to the power of suggestion as well as the drugs — or that communities less familiar with modern medicine misinterpreted the signs of mental illness. (There's actually a malady out there known as "Walking Corpse Syndrome," or Cotard Delusion, in which sufferers believe themselves to be dead.)
Other researchers continue to insist that a dose of tetrodotoxin, combined with the oxygen deprivation suffered while being buried alive, could explain at least some of the zombie cases reported in Haiti.
The evolution of zombies
Whether zombies arise from myth, malevolence or mental illness, they have clearly gotten a grip on our imagination — and scientists have several theories for why that's so. One theory has to do with the evolutionary advantage associated with being able to recognize friend vs. foe.
Our ancestors had to decide quickly whether the creature they encountered in the night was a fellow member of the tribe, or an enemy warrior, or an animal predator. Being able to sense when something wasn't right about a shadowy creature, and doing something about it quickly, could make the difference between survival and death.
Ayse Saygin, a neuroscientist at the University of California at San Diego, said it's particularly telling that the White Walkers and the wights on "Game of Thrones" have shining blue eyes. That's an obvious signal to the brain that something's not right. "Over time, we have adapted to recognize human eyes," she told NBC News. "At night, if you saw gleaming eyes, it could be a predator."
Zombies also play upon our ability to recognize who's healthy and who's not. "This is not my theory, but we can speculate that our response to zombies may be related to disease avoidance," she said.
'Uncanny valley' ahead
Saygin's specialty is exploring the "uncanny valley" — the cognitive area between obvious cartoon characters (such as Woody in the "Toy Story" movies) and real-life actors (such as Tom Hanks in "Forrest Gump"). In between, there's an eerie place where characters look too real to be made-up, but not real enough to be alive. Such characters "usually unnerve people," Saygin said. A good example of a character in the uncanny valley is the train conductor that looks almost, but not quite, like Tom Hanks in "Polar Express."
"We often use 'zombie-like' or 'creepy' to describe the uncanny valley," Saygin said.
Saygin suspects that our inner zombie detector has something to do with how a not-quite-right character triggers a "prediction violation" in our brain — that is, a sense that whatever you're looking at is not likely to act the way you'd expect it to act.
So how do the White Walkers and the wights on "Game of Thrones" rank on Saygin's creep-o-meter? She gives them a thumbs-up. The CGI-enhanced White Walkers are different enough from humans to be perceived as creepy in a good way, thanks to their ice-blue skin and blazing eyes. And even though the wights are not technically zombies, they're close enough to the "Walking Dead" archetype to trigger the right kind of spooky response.
"They're plausible dead people," Saygin said.
For still more scientific angles on "Game of Thrones," check out our reality checks on fire-breathing dragons, death by being burned alive, freakishly long winters, head transplants, lingering diseases and supposedly painless poisons. Got questions about "GoT"? Flag them with the Twitter hashtag #GOTscience.