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Why Are Our Brains Susceptible to Body Illusions?

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Are you bored with your body? Is bilateral symmetry feeling a little stale?

You’re in luck. You don’t need cyborg technology to give yourself an upgrade. Just grab a buddy, a towel, and a rubber hand. Line up your real hands and the fake hand on a table. Drape the towel over one arm and the rubber wrist so that it looks like you have two arms growing out of one shoulder. Then ask your friend to poke the hand on your mutant side with synchronized, unpredictable movements. As you watch, you will suddenly feel as if the rubber hand is your own.

Intrigued? You’re not alone. When a variant of the Third Hand Trick was discovered in the nineties, other psychologists jumped into the illusion game.

For inspiration, they turned to the classic Pinocchio Effect. By standing behind a friend and applying random, synched touches to the tip of your and your partner’s noses, you make it seem that you have sensation in your friend’s nose. When confronted with this bizarre scenario, your brain concludes that your nose must have stretched three feet. From there, things got Frankensteinian.

Using only a mirror, Dr. V. S. Ramachandran started resurrecting the lost limbs of amputees, thus relieving their excruciating phantom pain.

And Henrik Ehrsson began erasing the boundaries of the self. Using cameras, video goggles, and the synchronized poking technique of the Third Hand Illusion, you can now inhabit a mannequin, doll, or 30-foot dummy.

Not impressed? He can even strip you of your body entirely. Strap on some video goggles and position a camera behind you. While you stare at the back of your own head, have your some friends poke your chest and the camera’s stand in time. Soon, you’ll zip backwards out of your meat sack.

But how? How can a few seconds of trickery rewrite your body schema? It’s because you don’t have a fixed schema. Your brain is making it up as you go along. You perceive the world with two tools—bottom-up and top-down processing. Bottom-up processing starts with your senses and builds understanding from there. (Look, something white and round. Oh, it’s your mug.) Top-down processing applies assumptions to the environment. (Your mug is always on your desk, so that thing by your elbow must be your mug.)

You usually experience your body with top-down processing. There’s no reason to continually check that you haven’t sprouted a new hand. But body illusions challenge your assumptions. When the synchronicity of the poking makes it seem that you have nerves somewhere they don’t belong (a rubber hand, a friend’s nose, a reflection, a mannequin, a camera stand, etc), your bottom-up processing kicks into gear. It thinks, “If it has your nerves, it must be part of you!” Your top-down and bottom-up processes battle it out, and in most cases, bottom-up processing wins. But, really, you win.

Because if you ever do acquire a third hand, your brain will be ready.

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Big Questions
What Makes a Cat's Tail Puff Up When It's Scared?
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Cats wear their emotions on their tails, not their sleeves. They tap their fluffy rear appendages during relaxing naps, thrash them while tense, and hold them stiff and aloft when they’re feeling aggressive, among other behaviors. And in some scary situations (like, say, being surprised by a cucumber), a cat’s tail will actually expand, puffing up to nearly twice its volume as its owner hisses, arches its back, and flattens its ears. What does a super-sized tail signify, and how does it occur naturally without help from hairspray?

Cats with puffed tails are “basically trying to make themselves look as big as possible, and that’s because they detect a threat in the environment," Dr. Mikel Delgado, a certified cat behavior consultant who studied animal behavior and human-pet relationships as a PhD student at the University of California, Berkeley, tells Mental Floss. The “threat” in question can be as major as an approaching dog or as minor as an unexpected noise. Even if a cat isn't technically in any real danger, it's still biologically wired to spring to the offensive at a moment’s notice, as it's "not quite at the top of the food chain,” Delgado says. And a big tail is reflexive feline body language for “I’m big and scary, and you wouldn't want to mess with me,” she adds.

A cat’s tail puffs when muscles in its skin (where the hair base is) contract in response to hormone signals from the stress/fight or flight system, or sympathetic nervous system. Occasionally, the hairs on a cat’s back will also puff up along with the tail. That said, not all cats swell up when a startling situation strikes. “I’ve seen some cats that seem unflappable, and they never get poofed up,” Delgado says. “My cats get puffed up pretty easily.”

In addition to cats, other animals also experience piloerection, as this phenomenon is technically called. For example, “some birds puff up when they're encountering an enemy or a threat,” Delgado says. “I think it is a universal response among animals to try to get themselves out of a [potentially dangerous] situation. Really, the idea is that you don't have to fight because if you fight, you might lose an ear or you might get an injury that could be fatal. For most animals, they’re trying to figure out how to scare another animal off without actually going fisticuffs.” In other words, hiss softly, but carry a big tail.

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Big Questions
What Happened to the Physical Copy of the 'I Have a Dream' Speech?
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AFP, Getty Images

On August 28, 1963, Martin Luther King Jr. stood on the steps of the Lincoln Memorial and gave a speech for the ages, delivering the oratorical masterpiece "I Have a Dream" to nearly 250,000 people.

When he was done, King stepped away from the podium, folded his speech, and found himself standing in front of George Raveling, a former Villanova basketball player who, along with his friend Warren Wilson, had been asked to provide extra security around Dr. King while he was speaking. "We were both tall, gangly guys," Raveling told TIME in 2003. "We didn't know what we were doing but we certainly made for a good appearance."

Moved by the speech, Raveling saw the folded papers in King’s hands and asked if he could have them. King gave the young volunteer the speech without hesitation, and that was that.

“At no time do I remember thinking, ‘Wow, we got this historic document,’” Raveling told Sports Illustrated in 2015. Not realizing he was holding what would become an important piece of history in his hands, Raveling went home and stuck the three sheets of paper into a Harry Truman biography for safekeeping. They sat there for nearly two decades while Raveling developed an impressive career coaching NCAA men’s basketball.

In 1984, he had recently taken over as the head coach at the University of Iowa and was chatting with Bob Denney of the Cedar Rapids Gazette when Denney brought up the March on Washington. That's when Raveling dropped the bomb: “You know, I’ve got a copy of that speech," he said, and dug it out of the Truman book. After writing an article about Raveling's connection, the reporter had the speech professionally framed for the coach.

Though he displayed the framed speech in his house for a few years, Raveling began to realize the value of the piece and moved it to a bank vault in Los Angeles. Though he has received offers for King’s speech—one collector wanted to purchase the speech for $3 million in 2014—Raveling has turned them all down. He has been in talks with various museums and universities and hopes to put the speech on display in the future, but for now, he cherishes having it in his possession.

“That to me is something I’ll always be able to look back and say I was there,” Raveling said in the original Cedar Rapids Gazette article. “And not only out there in that arena of people, but to be within touching distance of him. That’s like when you’re 80 or 90 years old you can look back and say ‘I was in touching distance of Abraham Lincoln when he made the Gettysburg Address.’"

“I have no idea why I even asked him for the speech,” Raveling, now CEO of Coaching for Success, has said. “But I’m sure glad that I did.”

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