Original image

Why Are Our Brains Susceptible to Body Illusions?

Original image

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.

Original image
Big Questions
Why Don't We Eat Turkey Tails?
Original image

Turkey sandwiches. Turkey soup. Roasted turkey. This year, Americans will consume roughly 245 million birds, with 46 million being prepared and presented on Thanksgiving. What we don’t eat will be repurposed into leftovers.

But there’s one part of the turkey that virtually no family will have on their table: the tail.

Despite our country’s obsession with fattening, dissecting, and searing turkeys, we almost inevitably pass up the fat-infused rear portion. According to Michael Carolan, professor of sociology and associate dean for research at the College for Liberal Arts at Colorado State University, that may have something to do with how Americans have traditionally perceived turkeys. Consumption was rare prior to World War II. When the birds were readily available, there was no demand for the tail because it had never been offered in the first place.

"Tails did and do not fit into what has become our culinary fascination with white meat," Carolan tells Mental Floss. "But also from a marketing [and] processor standpoint, if the consumer was just going to throw the tail away, or will not miss it if it was omitted, [suppliers] saw an opportunity to make additional money."

Indeed, the fact that Americans didn't have a taste for tail didn't prevent the poultry industry from moving on. Tails were being routed to Pacific Island consumers in the 1950s. Rich in protein and fat—a turkey tail is really a gland that produces oil used for grooming—suppliers were able to make use of the unwanted portion. And once consumers were exposed to it, they couldn't get enough.

“By 2007,” according to Carolan, “the average Samoan was consuming more than 44 pounds of turkey tails every year.” Perhaps not coincidentally, Samoans also have alarmingly high obesity rates of 75 percent. In an effort to stave off contributing factors, importing tails to the Islands was banned from 2007 until 2013, when it was argued that doing so violated World Trade Organization rules.

With tradition going hand-in-hand with commerce, poultry suppliers don’t really have a reason to try and change domestic consumer appetites for the tails. In preparing his research into the missing treat, Carolan says he had to search high and low before finally finding a source of tails at a Whole Foods that was about to discard them. "[You] can't expect the food to be accepted if people can't even find the piece!"

Unless the meat industry mounts a major campaign to shift American tastes, Thanksgiving will once again be filled with turkeys missing one of their juicier body parts.

Have you got a Big Question you'd like us to answer? If so, let us know by emailing us at

Original image
Big Questions
Why Do We Dive With Sharks But Not Crocodiles?
Original image

Why do we dive with sharks but not crocodiles?

Eli Rosenberg:

The issue is the assumption that sharks' instincts are stronger and more basic.

There are a couple of reasons swimming with sharks is safer:

1. Most sharks do not like the way people taste. They expect their prey to taste a certain way, like fish/seal, and we do not taste like that. Sharks also do not like the sensation of eating people. Bigger sharks like great whites enjoy prey with a high fat-bone ratio like seals. Smaller sharks enjoy eating fish, which they can gobble in one bite. So, while they might bite us, they pretty quickly decide “That’s not for me” and swim away. There is only one shark that doesn’t really care about humans tasting icky: that shark is our good friend the tiger shark. He is one of the most dangerous species because of his nondiscriminatory taste (he’s called the garbage can of the sea)!

2. Sharks are not animals that enjoy a fight. Our big friend the great white enjoys ambushing seals. This sneak attack is why it sometimes mistakes people for seals or sea turtles. Sharks do not need to fight for food. The vast majority of sharks species are not territorial (some are, like the blacktip and bull). The ones that are territorial tend to be the more aggressive species that are more dangerous to dive with.

3. Sharks attacked about 81 people in 2016, according to the University of Florida. Only four were fatal. Most were surfers.

4. Meanwhile, this is the saltwater crocodile. The saltwater crocodile is not a big, fishy friend, like the shark. He is an opportunistic, aggressive, giant beast.

5. Crocodiles attack hundreds to thousands of people every single year. Depending on the species, one-third to one-half are fatal. You have a better chance of survival if you played Russian roulette.

6. The Death Roll. When a crocodile wants to kill something big, the crocodile grabs it and rolls. This drowns and disorients the victim (you). Here is a PG video of the death roll. (There is also a video on YouTube in which a man stuck his arm into an alligator’s mouth and he death rolled. You don’t want to see what happened.)

7. Remember how the shark doesn’t want to eat you or fight you? This primordial beast will eat you and enjoy it. There is a crocodile dubbed Gustave, who has allegedly killed around 300 people. (I personally believe 300 is a hyped number and the true number might be around 100, but yikes, that’s a lot). Gustave has reportedly killed people for funsies. He’s killed them and gone back to his business. So maybe they won’t even eat you.

8. Sharks are mostly predictable. Crocodiles are completely unpredictable.

9. Are you in the water or by the edge of the water? You are fair game to a crocodile.

10. Crocodiles have been known to hang out together. The friend group that murders together eats together. Basks of crocodiles have even murdered hippopotamuses, the murder river horse. Do you think you don't look like an appetizer?

11. Wow, look at this. This blacktip swims among the beautiful coral, surrounded by crystal clear waters and staggering biodiversity. I want to swim there!

Oh wow, such mud. I can’t say I feel the urge to take a dip. (Thanks to all who pointed this out!)

12. This is not swimming with the crocodiles. More like a 3D aquarium.

This post originally appeared on Quora. Click here to view.


More from mental floss studios