This morning, the World Health Organization revised its health guidelines around the consumption of meat. The report from the WHO’s International Agency for Research on Cancer now labels processed meats as “carcinogenic to humans,” meaning their consumption can cause cancer. The report also classifies red meat as “probably carcinogenic to humans.”

For more on what this finding means for our shopping list and diet choices, we’ve prepared a list of FAQs, as formulated by the collective minds of the PBS NewsHour.

What counts as red meat? What counts as processed meat?

Red meat is any meat that comes from a mammal. That means meat from cows (beef and veal), pigs (pork), sheep (lamb and mutton), horses, goats and bison all count as red meat.

White meats come from fish and poultry. The color difference is dictated by the amount of blood in the tissue, which plays into why red meat is more likely to cause cancer (see below).

Processed meats are any meats that aren’t fresh. People typically think of processed meat as only referring to pork and beef, but this category can also include poultry (chicken, turkey, duck) and fish. A processed meat, according to the panel, has been modified from its natural state, either “through salting, curing, fermentation, smoking, or other processes to enhance flavour or improve preservation.”

This includes sausages, hot dogs, corned beef, beef jerky, canned meat, meat sauces, lunch meats and bacon.

What does cancer “link” versus cancer “cause” mean?

The word “caused” sounds much more definitive than “linked,” right? Consider the news headlines surrounding this report. Here are two examples:

W.H.O. Report Links Some Cancers With Processed or Red Meat (New York Times)

“Bad Day For Bacon: Processed Red Meats Cause Cancer, WHO Says (NPR)

So which is it?

Technically, meat consumption has been linked to cancer, especially colorectal cancer, for years. It’s a correlation or “link” backed by statistical evidence. Large-scale studies from Europe, Australia, Japan and the U.S. have shown that people who consume more processed and red meat are more likely to develop cancer. Meanwhile, research in the lab has shown scientifically — in rat models and human cells (see below) — how that meat leads to the chemical shifts and genetic mutations that turn healthy cells into cancer cells.

Based on this collective evidence, the WHO panel has concluded today that processed meat can cause cancer, upgrading its threat assessment from correlative to causal.

In contrast, red meat without processing remains a probable cancer-causing agent, because there is less evidence in humans showing that it can spawn cancer.

In a separate Q&A, the WHO wrote:

In the case of red meat, the classification is based on limited evidence from epidemiological studies showing positive associations between eating red meat and developing colorectal cancer as well as strong mechanistic evidence.

Limited evidence means that a positive association has been observed between exposure to the agent and cancer but that other explanations for the observations (technically termed chance, bias, or confounding) could not be ruled out.

How does processed meat compare to smoking and other carcinogens?

The IARC deals in strength of evidence. For this agency, scientific evidence either points to a compound causing cancer in humans or it doesn’t. To classify carcinogenic status, it separates agents into five groups:

Group 1 – carcinogenic to humans

Group 2A – probably carcinogenic to humans

Group 2B – possibly carcinogenic to humans

Group 3- not classifiable

Group 4 – probably not carcinogenic

Of the millions of chemicals in the world, the WHO only only 118 agents fall into group 1. This group includes tobacco smoke, asbestos, aflatoxins (a chemical sometimes found in organic peanut butter), coal emissions from indoor stoves and as of this morning, processed meat.

However, the number of cases caused by each of these agents — or their cancer risk among the general population — varies. That’s because risk, from a public health perspective, is a statistical property. For instance, check out the Cancer Research UK’s breakdown of how smoking and meat consumption contribute to overall cancer rates in the UK:

Tobacco vs meat – what’s the risk? More on our blog: https://t.co/5AtIzFwEKh pic.twitter.com/o2heo1OLDa

— Cancer Research UK (@CR_UK) October 26, 2015

The risk — the statistical rate in the population — of developing cancer is greater for smoking tobacco than eating processed meat.

Ed Yong’s piece in The Atlantic does a great job of outlining why WHO’s categorical danger versus actual statistical risk can sometimes breed confusion.

My grandpa ate 7 lbs of red meat every day and lived to be 130. Why didn’t he get cancer?

It’s impossible to determine if an individual will get cancer based on a lifestyle choice, whether it’s smoking or eating processed meat. Cancer occurs when a healthy cell acquires enough mutations to start replicating uncontrollably and to spread into new organs away from its site of origin.

Those mutations vary dramatically among the types of cancer (lung, pancreatic, colorectal, etc). They can even differ within a subtype, meaning a pancreatic cancer from one person can be genetically dissimilar than a pancreatic cancer in another. Plus, a malignant tumor in a single individual is constantly evolving, and there is evidence suggesting no two cancer cells in the same tumor are the same.

A cell’s ability to acquire these mutations depends on personal genetics — whether or not you inherited a predisposition from mom and dad — and exposure to compounds that are genotoxic; that is, that can change your DNA.

The IARC is merely concluding today that processed meat can cause cancer if given the chance.

How much processed meat is safe to eat?

On an individual level, it’s hard to say. On a population level, the WHO report cites this epidemiology meta analysis, which examined colorectal cancer studies going back to 1966.

Based on that study, a person who eats 50 grams per day of processed meat has an 18 percent higher chance of developing colorectal cancer. A person who eats 100 grams has a 36 percent higher chance and so on. According to Cancer Research UK, 50 grams per day would be on par with two slices of ham. Two slices of bacon is about 75 grams.

Eating too much meat? Tips on cutting down, plus more on our blog https://t.co/5AtIzFwEKh pic.twitter.com/i12S4kzQDE

— Cancer Research UK (@CR_UK) October 26, 2015

For red meat, cancer risk elevates by 17 percent for every 100 grams per day that is consumed.

When cancer risk levels of both processed meat and red meat were modeled together, the relationship maxed out at 140 grams per day.

Are organically raised meats as dangerous as industrial-produced?

In the context of this WHO report, yes. The danger posed by processed meat and red meat comes from chemical properties inherent to all forms of meat (see below). Organic meat labeling, at least according to the USDA, tackles issues like antibiotic use, hormone use, and access to exercise for domestic animals, which falls outside the scope of the WHO’s report.

What about white meats (chicken and fish) that are processed? Like smoked salmon? What about nitrate-free meats?

The scientific connection between smoked, salted, or cured meats comes down to how these preservation processes influence the chemistry of these foods.

Curing meats involves adding salt, sugar, nitrates like saltpeter or nitrites to preserve foods against bacteria-induced rot and maintain flavor, though the most validated suspects in the cancer drama are nitrites. Enzymes in meat convert nitrites into nitrogen oxide and nitrous acid. Both of which can chemically react with amino acids found in our proteins to form N-nitroso-compounds (NOCs), a class of carcinogenic compounds also sometimes described under the banner nitrosamines. Though saltpeter and other nitrates are a somewhat antiquated way of curing meats, these compounds can become nitrites thanks to chemical reactions mediated by our own cells, by bacteria in our guts, or by bacteria naturally found in meat. NOCs are also spawned by chemical reactions with heme, the red pigment/compound responsible for binding oxygen in blood cells.

“For the red meat, they think it is the HEME iron that is damaging,” said Alice Bender, director of Nutrition Programs at American Institute for Cancer Research.

NOCs can physically bind to genetic material — forming what are called DNA adducts — which can initiate the transformation of healthy cells into a cancer cells.

Grilling, barbecuing, frying, broiling or any form of cooking contributes to the carcinogenic potential of meat due to the accumulation of polycyclic aromatic hydrocarbons (PAHs). How this accumulation happens isn’t completely understood, but this 2005 review paper offers a general overview of the current thinking. In sum, it states that heat breaks down complex organic compounds naturally found in muscle tissue — like fats and sugars — into smaller compounds that react to form PAHs:

At high temperatures, organic compounds are easily fragmented into smaller compounds, mostly free radicals, which may then recombine to form a number of relatively stable PAHs. At temperatures below 400 °C, only small amounts of PAHs are formed. However, the amounts of PAHs increase linearly in the range 400–1000 °C.

Excessive heat can also introduce carcinogens to meat in the form of heterocyclic aromatic amines, which the WHO report abbreviates as HAAs. (The term HCA is also used and means the same thing.) Heterocyclic aromatic amines are formed when naturally-occurring compounds like creatine (found in high quantities in muscle meats), amino acids in protein and sugars become too hot. Like NOCs, heterocyclic aromatic amines are genotoxic and can yield mutations that cause cancer. Here’s what the 2005 review had to say about the formation of heterocyclic aromatic amines:

In general pan-frying and grilling produce high yield of HCAs at cooking temperatures from 200 °C and above, boiling yields little or no HCAs, and deep-fat frying, roasting, and baking procedure give variable yields. Extremely high yield of HCAs have been reported in pan residues….from frying, roasting or baking, while most commercial bouillon cubes contain modest amounts.

PAHs are also thought to be produced when fat and juices from meat hit flames over open grills. These PAHs then float up and “adhere to the surface of meat,” according to the National Cancer Institute.

Smoking introduces carcinogens to meat in the form of polycyclic aromatic hydrocarbons created in the fumes of burning wood or by heat.

These food prep processes increase the amounts of these carcinogenic chemicals in meat, regardless of whether the original animal was a mammal, a bird or a fish. However, the WHO panel primarily made their assessment based on research into processed red meats.

However, given the limited number of studies that have independently examined the influence of different preservation methods on cancer risk among the general population, the WHO can’t state yet if one is worse than another:

Different preservation methods could result in the formation of carcinogens (e.g. N-nitroso compounds), but whether and how much this contributes to the cancer risk is unknown.[Also] there were not enough data for the IARC Working Group to reach a conclusion about whether the way meat is cooked affects the risk of cancer.

Should you give up meat?

Not necessarily. Alice Bender, director of Nutrition Programs at American Institute for Cancer Research, said it’s important to remember the distinction that the WHO report makes between processed meat and red meat.

“Processed meats even in small amounts were increasing risk — a little less than 2 ounces [which is equivalent to] a hot dog or few slices of cold cuts,” Bender told the NewsHour. “For red meat, what is important to keep in mind isn’t so much that you shouldn’t eat it at all, but more the amounts. It’s large amounts that become harmful.”

Oncologist John Schoenfeld of Harvard Medical School agreed.

“There are benefits to red meat, and the findings don’t say that a balanced diet that includes red meat is bad,” Schoenfeld said. “[The report] gives pause to the part of the American diet that is high in meat consumption and red meat. There needs to be broader discussion on [red meat], weighing the benefits and the risks.”

For more of our conversation with John Schoenfeld, check out his interview with PBS NewsHour correspondent William Brangham.

If you have a question, leave it in the comments. We’ll address them ASAP.

Rhana Natour contributed to this report.

Still have questions about Monday’s news from World Health Organization? Join us at 1 p.m. EDT Wednesday for a Twitter chat. Joining us to take your questions will be Alice Bender from the American Institute for Cancer Research (@aicrtweets) and NPR Food and Culture Correspondent, Alison Aubrey (@AubreyNPRFood).

Leave your questions for these experts in the comments below, or on Twitter using the hashtag #NewshourChats.

The post FAQ: Exactly what processed meat should I avoid, and other questions appeared first on PBS NewsHour.

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In our NewsHour Shares series, we show you things that caught our eye recently on the web. What about you? Leave your suggestions in the comments below, or tweet to @NewsHour using #NewsHourShares. We might share it on air.

GWEN IFILL: And now to our NewsHour Shares of the day, something that caught our eye which might be of interest to you, too.

A NASA spacecraft today flew into an icy spray coming off one of Saturn’s moons. The mission? To figure out whether that moon has what they call hydrothermal vents that could support life. This NASA video explains the science behind the theories.

The post Flying through an icy plume to test a moon’s hospitality appeared first on PBS NewsHour.

Actors dressed as martians for their roles in the show “The Man in the Moon,” at the London Palladium in January 1964, walk across Regent Street as two policemen watch them. Photo by Chris Ware via Getty Images

Human interest in unidentified flying objects (UFOs) dates back thousands of years. In the winter of 214 BC, ancient historian Livy reported phantom ships in the skies of Rome. Ancient stargazers believed the neighboring planets in our solar system housed the gods.

Just this month, scientists published data on an unusual spectral pattern coming from the star KIC 8462852 — or Tabby’s Star. In an article, the Atlantic highlighted one scenario that might explain the pattern: the possibility of alien megastructures. Despite follow-up stories describing more logical scenarios — a giant cloud of comets or a jelly bean-shaped star — much of the mainstream fervor focused on possibilities of alien life. Even two days after the Atlantic piece dropped, one of the scientists behind the KIC 8462852 study told Business Insider that the media coverage had gotten “a bit out of hand” and the probability that the signal comes from aliens is “very low.”

“Just to clarify, neither [my colleague] Jason [Wright] or myself … are advocating that it is an alien megastructure, but we also can’t completely rule it out,” Penn State astronomer Kimberly Cartier told Business Insider.

Smart people believe in aliens too. Renowned Harvard University psychiatrist and Pulitzer-prize winner John E. Mack believed in alien abductions until his death in 2004. (Vanity Fair wrote a great profile of Mack two years ago). Thirty years ago, the famed psychoanalyst C.G. Jung blamed the fear of the unknown, and with it, the human preoccupation with aliens, on our innate search for meaning in places where none exists. In a 2010 essay, clinical psychologist Stephen Diamond described the mental phenomenon this way:

…it is precisely the profoundly mysterious and mythic nature of UFO’s that, like dreams, makes them so psychologically powerful. As with all natural or metaphysical phenomena, once science dissects, analyzes and mechanistically explains such mysteries, their numinous, spiritual, potentially healing power is deadened or lost.

In the spirit of the profoundly mysterious (and Halloween!), PBS NewsHour brings you seven bizarre events originally linked to aliens but then ultimately explained by science. Readers are free to believe what they want, but in these cases, a logical explanation seems more plausible…or at least that’s what THEY want us to tell you.

Phone calls from E.T.

Man dressed in alien costume looking at mobile. Photo by Tara Moore

In 1967, a 24-year-old astronomer and graduate student named Jocelyn Bell detected rhythmic pulses among data collected by her radio telescope. As the American Physical Society describes:

Working at the Mullard Radio Astronomy Observatory, near Cambridge, starting in 1965 Bell spent about two years building the new telescope, with the help of several other students. Together they hammered over 1,000 posts, strung over 2,000 dipole antennas between them, and connected it all up with 120 miles of wire and cable. The finished telescope covered an area of about four and a half acres.

Within a few weeks Bell noticed something odd in the data, what she called a bit of “scruff.” The signal didn’t look quite like a scintillating source or like manmade interference. She soon realized it was a regular signal, consistently coming from the same patch of sky.

Bell and her mentor Anthony Hewish initially thought the signals were a phone call from an extraterrestrial civilization. But further investigation revealed a previously unknown celestial object: a neutron star. Bell’s initial data had caught focused beams of electromagnetic radiation, which would come to be called pulsars. The work would share the 1974 Nobel Prize in Physics. Bell’s name wasn’t included in the award, but her work inspired the detection protocols for scientific institutes that work in the search for extraterrestrial intelligence.

The SETI Detection Protocols aren’t legally binding, but they dictate how scientists will verify a communication from aliens and the suggested practices for informing the public.

Radio signals represent one of our best bets for spotting extraterrestrial life, and they’ve led to multiple false alarms over the years, such as The Wow! Signal in 1977.

However, a study published this April reported that a search of the 100,000 closest galaxies has come up empty handed with regards to detecting the electromagnetic signals that would indicate advanced technology. That doesn’t eliminate the possibility of alien life using modes of technology beyond our means of detection, but for now, we’re still waiting for E.T.’s call.

Face on Mars

NASA’s Viking 1 Orbiter spacecraft shot this image of Mars on July 25, 1976. Can you make out a face from the eroded rock? Image courtesy of NASA/JPL

While circling Mars in 1976, NASA’s Viking 1 spacecraft snapped photos of the Red Planet’s landscape. Among the images it beamed back was a picture of a mile-wide landform that resembled a face.

Known as the “Face of Mars,” the image prompted arguments that the site was evidence of an ancient civilization on the planet.

NASA, in its caption for the image, said the mesa-like formation looked like a human head, “giving the illusion of eyes, nose and mouth.” And while the space agency never said the photo captured anything other than a rocky landform jutting from Mars, it left conspiracy theorists wondering whether NASA was hiding something.

But the “face” is not a sign of intelligent Martian life. It’s your brain tricking you. Or, rather, it’s your brain perceiving a meaningful stimulus, like a face, out of everyday objects or sounds. This is a phenomenon called pareidolia, and these moments usually appear in the Weird News section, such as a face in a cliff, the Man in the Moon, or the Virgin Mary on a burnt tortilla.

A 2014 study published in the journal Cortex concluded that the phenomenon was a healthy, common occurrence.

“Most people think you have to be mentally abnormal to see these types of images, so individuals reporting this phenomenon are often ridiculed,” said lead researcher Kang Lee of the University of Toronto. “But our findings suggest that it’s common for people to see non-existent features because human brains are uniquely wired to recognize faces, so that even when there’s only a slight suggestion of facial features the brain automatically interprets it as a face.”

The study added that the brain’s ability to glean faces from ambiguous information is “highly adaptive” because of the “supreme importance of faces in our social life and the high cost resulting from failure to detect a true face.”

This is a hi-res image of the same “face” that NASA captured in 1976. There’s not a human face there anymore. Image courtesy of NASA/JPL/University of Arizona

NASA, equipped with modern technology, reshot the “Face of Mars” in 1998. In the higher resolution, the face disappeared. NASA was right in its original caption: The “face” is an illusion.

Alien engineering

Tourists ride camels in front of Giza pyramids in 2006. Humans were perfectly capable of building these ancient wonders. Photo by Goran Tomasevic/Reuters

The Great Pyramid of Giza, one of the original Seven Wonders, is such a paragon of human achievement, that people have questioned whether the ancient, man-made structure was actually constructed with the help of aliens.

But give the ancient Egyptians some credit.

According to architect Jean-Pierre Houdin and Egyptologist Bob Brier, the ancient Egyptians hauled 2.5 ton limestone blocks using an internal ramp that snaked up the pyramid like a parking garage.

In 1986, a French team failed to find any hidden spaces in the Giza pyramid that suggested an internal ramp. But, as documented in this National Geographic TV special, one of the French researchers met with Houdin 15 years later to reveal a diagram left out of that 1986 study. The diagram showed a hollow spiral shape within the pyramid that appeared to support Houdin’s theory.

Despite the mounting evidence to the contrary, people also continue to believe that primitive cultures were not able to erect pyramids in Nigeria, China or Indonesia without extraterrestrial assistance.

“It’s these suggestions that are really denigrating the people whose names, bodies, family relationships, tools and bakeries we actually find,” Egyptologist Mark Lehner, who studied the pyramids for years and wrote “The Complete Pyramids,” told NOVA in 1997.

“Everything that I have found convinces me more and more that indeed it is this society that built the Sphinx and the Pyramids,” he said. “Every time I go back to Giza, my respect increases for those people and that society, that they could do it.”

Flying Saucers

Nevada Governor Bob Miller presides over the unveiling of a new road sign for Nevada State Highway 375 on April 18, 1996, about 150 miles north of Las Vegas. The highway has been the location for numerous UFO sightings, possibly related to the close proximity of the secret U.S. airbase Area 51. Photo by Reuters

“I have no doubt that UFOs exist,” science writer and longtime investigator of unusual phenomena Benjamin Radford wrote for Space.com.

That’s because an Unidentified Flying Object is any vision in the sky that a person’s mind can’t immediately explain. But that doesn’t mean it’s piloted by alien life. The Earth’s atmosphere is bombarded by roughly 100 tons of space rock every day, and who hasn’t seen a saucer-shaped cloud in their lifetime?

The origins of the term “flying saucer” can be traced to a single, misquoted source.

The Eastern Oregonian reported on June 24, 1947, that Idaho pilot Kenneth Arnold saw nine “flying objects” or flashes that flew past Mount Rainier, according to this Atlantic report. But when Arnold’s story got picked up by other news outlets, the description of the objects morphed into “flying saucers.”

Years later, Arnold said he had told the Oregonian that the objects “flew like a saucer would if you skipped it across the water.” In other words, Arnold said he used “saucer” to describe the movement — and not the shape — of the UFOs.
In a 1950 interview with journalist Edward R. Murrow, Arnold repeated his claim that reporters had misquoted him.

“[W]hen I told the press, they misquoted me, and in the excitement of it all, one newspaper and another one got it as ensnarled up that nobody knew just exactly what they were talking about, I guess,” he told Murrow.

Kenneth Arnold submitted this letter, complete with rough sketches of the flying objects he saw, to the Army Air Force on July 12, 1947. Image courtesy of Wikimedia Commons

Either way, the era of UFO sightings had begun, and the flying saucer became a mainstay in science fiction.

Only weeks later, rancher William Brazel discovered a wreckage near Roswell, New Mexico and assumed a flying saucer had crashed. That Roswell incident would become America’s best known experience with UFOs. On July 8, military officials claimed the debris came from a weather balloon, but decades later the incident would resurface as a centerpiece in a government alien cover-up, as detailed by the Committee of Skeptical Inquiry.

The government was covering up the true reason for the wreckage, but it wasn’t aliens. The real reason involved Project MOGUL, a spy balloon built to detect long-range soundwaves from possible Soviet nuclear weapons.

Researchers believe the Cold War continued to fuel UFO hysteria, as the Guardian reported in 2002:

Many of the early UFO sightings were seemingly confirmed by Britain’s fledgling radar system, often scrambling fighter planes into the sky to investigate sightings. But, as the new technology improved, the number of incidents appearing on radar quickly dwindled to zero. ‘That cannot be a coincidence. Those early confirmations were just a product of a primitive radar system,’ Clarke said.

Missiles continue to be identified as UFOs, as do things like Chinese lanterns, oddly-shaped clouds, lightning sprites and the planet Venus.

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UFO sightings often involve hole-punch clouds like this one, which typically occur when an airplane creates small snowstorm while passing through a cloud.

Crop circles

A crop circle appeared in London’s Kew Gardens on Sept. 19, 2002. Photo by Reuters

No one disputes that crop circles are real. But who created them?

Appearing first in the late 1970s in the English countryside, conspiracies often pointed to aliens sending messages to humans in fields of flattened crops. Instead, it was an Earthbound hoax.

After years of crop circle reports in southern England in the 1980s, crop circles began popping up in Canada and Australia too. But then, two pranksters in their 60s came forward in 1991 as the originators of a massive hoax.

WHEN David Chorley and Doug Bower told the London tabloid Today in 1991 that they made the circular designs overnight by using wooden planks, a ball of string, and a piece of wire attached to a baseball cap that worked as a sighting device.

In the video below, Chorley and Bower explained how they could make a circle 80 to 90 feet wide in 10 minutes, adding that they didn’t see news reports of their crop circles until three years after their initial creation.

Video by YouTube user mdftrasher

The hoaxers said they decided to confess when Bower’s wife became suspicious of the high mileage on the couple’s car. She suspected her husband was having an affair.Bower explained that he and Chorley flattened crops in southern England as many as 30 times a year. And the crop circles spotted outside their home country? That was the work of copycats.

The confessions, however, didn’t dissuade M. Night Shyamalan from featuring the crop circles in his 2002 movie “Signs.”

Area 51

Area 51 border and warning sign stating that “photography is prohibited.” Photo by Flickr user X 51

For decades, conspiracy theories painted the hyper-exclusive, top secret military base near Groom Lake, Nev., as a storage bin for U.S. scientists to study little green men and their alien spacecraft.

Then in 2013, the CIA, prompted by a public records request by the National Security Archive, declassified a 400-page 1992 document that specifically acknowledged the existence of Area 51.

Or, as one UFO enthusiast told NBS News: “They say Area 51 is real? Duh!”

In fact, Annie Jacobsen, author of “Area 51: An Uncensored History of America’s Top Secret Military Base,” told National Geographic that only one page of the declassified report was new information. That one page literally put Area 51 on a map.

But a lot remains unknown about the remote government facility. The declassified report goes on about the U-2 spy planes used during the Cold War that were being tested at the site. There’s no mention of Roswell aliens, spaceships and the like.

The report, however, does mention UFOs, but only that the U-2 planes “led to an unexpected side effect — a tremendous increase in reports of unidentified flying objects, UFOs.”

Alien Abductions

Alien abduction warning signs are posted in the AlienVault booth during the Black Hat USA 2015 cybersecurity conference in Las Vegas. Photo by Steve Marcus/Reuters

Alien abductions have been reported across the globe, and these claims may have a neuroscientific explanation.

Our memories are prone to change and susceptible to the inclusion of false facts, which is known as false memory recall. False memory recall is common. This mental behavior can muck up eyewitness testimony and gets worse as we age. Just within the last two years, scientists have shown that they can artificially implant a false memory into the brains of mice.

A 2003 Harvard study showed that people who claim alien abductions are more susceptible to false memories. Plus their memory recall is often so strong and so physically disturbing that it is comparable to war veterans remembering battle.

Sleep paralysis is a possible explanation for how these memories form in the first place. Sleep paralysis occurs when someone’s brain wakes up before the rest of the body. During REM sleep, the body releases a chemical that prevents it from moving while you sleep. During a sleep paralysis episode, a person can become conscious before the chemical wears off. Cue the monsters that emerge from the dreams that occur somewhere in that accidental space.

“Sleep paralysis is common and no more indicative of mental illness than a hiccup, the researchers point out. But when the hallucination and paralysis occur together, many people find the combination frightening, and they attempt to find a meaning in it,” William Cromie wrote in the Harvard Gazette.

According to a 2011 study by Pennsylvania State University, as many as 7.6 percent of the general population will experience at least one instance of sleep paralysis in their lifetime.

When falling asleep or waking up, people have reported faceless shadowy figures or a dark presence in their bedrooms. Horrifically, these harbingers of doom would sometimes advance toward them while they’re unable to move.

While it’s not the work of supernatural beings, it is a brain glitch that produces some serious fuel for nightmares.

The post 7 times that science explained aliens appeared first on PBS NewsHour.