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Jaysin Trevino, Flickr // CC BY 2.0
Jaysin Trevino, Flickr // CC BY 2.0

Does Cracking Your Knuckles Really Give You Arthritis?

Jaysin Trevino, Flickr // CC BY 2.0
Jaysin Trevino, Flickr // CC BY 2.0

You’ve heard it before. You’re in a quiet room in among a gathering of people, and then—POP!—a little cracking noise rings out, followed by another, and another, and another. For some, cracking knuckles is a habit, while for others that little pop brings relief. And it's not just reserved for tough guys before they beat people up: Between 25 and 54 percent of all people crack their knuckles multiple times a day. But is the old wives’ tale true? Are these knuckle-crackers more likely to hurt their hands and gradually develop arthritis as they get older? 

In short, nope! Despite the rumor that kids constantly hear, it turns out there is no scientific correlation between cracking your knuckles and developing arthritis in your joints, which is when one or more of the points where your bones meet develop inflammation. 

When you crack your knuckles, you're actually doing more bursting than cracking. The popping noise you hear is caused by small bubbles bursting in your synovial fluid, a yolk-like substance that lubricates the areas between bones and reduces friction for ease of movement.

Here's how it works: When you make the motion to crack your knuckles—either by stretching your fingers or bending them backwards—you expand the joint. This causes the pressure between the joint  to decrease, as well as the ligaments that connect the bones and the joint capsule that holds all of it together. That depressurization causes gasses like carbon dioxide, nitrogen, and oxygen that are dissolved in the synovial fluid to form into little bubbles that rush into the empty space. As the joints settle back into place, the fluid also returns to its rightful place and pops those little bubbles, causing that recognizable cracking sound. 

The sensation of cracking your fingers feels good because the stretching of the joint also stimulates nerve endings found along the fingers; joints can’t be cracked more than once within 15 minutes to a half hour, which is about how long it takes for those gasses to dissolve back into your synovial fluid.

Among the scientific studies conducted to prove that there is no correlation between cracking your knuckles and osteoarthritis, one published in the Journal of the American Board of Family Medicine in 2010 found that, among a group of 215 participants between the ages of 50 and 89, arthritis was prevalent in about 18 percent of the people who crack their knuckles and in 21.5 percent who don't, making any correlation inconclusive. Probably the most entertaining study on the subject is by a Dr. Donald Unger who, inspired by his mother’s warnings as a child about getting arthritis by constantly cracking his knuckles, spent more than 60 years cracking only the knuckles on his left hand at least twice a day (in this case, the right hand served as his control). His finding, published in 1998 in a journal called Arthritis & Rheumatism, found there was no discernible sign of arthritis in his left hand as opposed to his right.

So don’t listen to what mom says, everybody—feel free to crack away!

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Big Questions
Why Do Cats 'Blep'?
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As pet owners are well aware, cats are inscrutable creatures. They hiss at bare walls. They invite petting and then answer with scratching ingratitude. Their eyes are wandering globes of murky motivations.

Sometimes, you may catch your cat staring off into the abyss with his or her tongue lolling out of their mouth. This cartoonish expression, which is atypical of a cat’s normally regal air, has been identified as a “blep” by internet cat photo connoisseurs. An example:

Cunning as they are, cats probably don’t have the self-awareness to realize how charming this is. So why do cats really blep?

In a piece for Inverse, cat consultant Amy Shojai expressed the belief that a blep could be associated with the Flehmen response, which describes the act of a cat “smelling” their environment with their tongue. As a cat pants with his or her mouth open, pheromones are collected and passed along to the vomeronasal organ on the roof of their mouth. This typically happens when cats want to learn more about other cats or intriguing scents, like your dirty socks.

While the Flehmen response might precede a blep, it is not precisely a blep. That involves the cat’s mouth being closed while the tongue hangs out listlessly.

Ingrid Johnson, a certified cat behavior consultant through the International Association of Animal Behavior Consultants and the owner of Fundamentally Feline, tells Mental Floss that cat bleps may have several other plausible explanations. “It’s likely they don’t feel it or even realize they’re doing it,” she says. “One reason for that might be that they’re on medication that causes relaxation. Something for anxiety or stress or a muscle relaxer would do it.”

A photo of a cat sticking its tongue out
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If the cat isn’t sedated and unfurling their tongue because they’re high, then it’s possible that an anatomic cause is behind a blep: Johnson says she’s seen several cats display their tongues after having teeth extracted for health reasons. “Canine teeth help keep the tongue in place, so this would be a more common behavior for cats missing teeth, particularly on the bottom.”

A blep might even be breed-specific. Persians, which have been bred to have flat faces, might dangle their tongues because they lack the real estate to store it. “I see it a lot with Persians because there’s just no room to tuck it back in,” Johnson says. A cat may also simply have a Gene Simmons-sized tongue that gets caught on their incisors during a grooming session, leading to repeated bleps.

Whatever the origin, bleps are generally no cause for concern unless they’re doing it on a regular basis. That could be sign of an oral problem with their gums or teeth, prompting an evaluation by a veterinarian. Otherwise, a blep can either be admired—or retracted with a gentle prod of the tongue (provided your cat puts up with that kind of nonsense). “They might put up with touching their tongue, or they may bite or swipe at you,” Johnson says. “It depends on the temperament of the cat.” Considering the possible wrath involved, it may be best to let them blep in peace.

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

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Big Questions
What Is Foreign Accent Syndrome?
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One night in 2016, Michelle Myers—an Arizona mom with a history of migraines—went to sleep with a splitting headache. When she awoke, her speech was marked with what sounded like an British accent, despite having never left the U.S. Myers is one of about 100 people worldwide who have been diagnosed with Foreign Accent Syndrome (FAS), a condition in which people spontaneously speak with a non-native accent.

In most cases, FAS occurs following a head injury or stroke that damages parts of the brain associated with speech. A number of recent incidences of FAS have been well documented: A Tasmanian woman named Leanne Rowe began speaking with a French-sounding accent after recovering from a serious car accident, while Kath Lockett, a British woman, underwent treatment for a brain tumor and ended up speaking with an accent that sounds somewhere between French and Italian.

The first case of the then-unnamed syndrome was reported in 1907 when a Paris-born-and-raised man who suffered a brain hemorrhage woke up speaking with an Alsatian accent. During World War II, neurologist Georg Herman Monrad-Krohn compiled the first comprehensive case study of the syndrome in a Norwegian woman named Astrid L., who had been hit on the head with shrapnel and subsequently spoke with a pronounced German-sounding accent. Monrad-Krohn called her speech disorder dysprosody: her choice of words and sentence construction, and even her singing ability, were all normal, but her intonation, pronunciation, and stress on syllables (known as prosody) had changed.

In a 1982 paper, neurolinguist Harry Whitaker coined the term "foreign accent syndrome" for acquired accent deviation after a brain injury. Based on Monrad-Kohn's and other case studies, Whitaker suggested four criteria for diagnosing FAS [PDF]:

"The accent is considered by the patient, by acquaintances, and by the investigator to sound foreign.
It is unlike the patient’s native dialect before the cerebral insult.
It is clearly related to central nervous system damage (as opposed to a hysteric reaction, if such exist).
There is no evidence in the patient’s background of being a speaker of a foreign language (i.e., this is not like cases of polyglot aphasia)."

Not every person with FAS meets all four criteria. In the last decade, researchers have also found patients with psychogenic FAS, which likely stems from psychological conditions such as schizophrenia rather than a physical brain injury. This form comprises fewer than 10 percent of known FAS cases and is usually temporary, whereas neurogenic FAS is typically permanent.

WHAT’S REALLY HAPPENING?

While scientists are not sure why certain brain injuries or psychiatric problems give rise to FAS, they believe that people with FAS are not actually speaking in a foreign accent. Instead, their neurological damage impairs their ability to make subtle muscle movements in the jaw, tongue, lips, and larynx, which results in pronunciation that mimics the sound of a recognizable accent.

"Vowels are particularly susceptible: Which vowel you say depends on where your tongue is in your mouth," Lyndsey Nickels, a professor of cognitive science at Australia's Macquarie University, wrote in The Conversation. "There may be too much or too little muscle tension and therefore they may 'undershoot' or 'overshoot' their target. This leads to the vowels sounding different, and sometimes they may sound like a different accent."

In Foreign Accent Syndromes: The Stories People Have to Tell, authors Nick Miller and Jack Ryalls suggest that FAS could be one stage in a multi-phase recovery from a more severe speech disorder, such as aphasia—an inability to speak or understand speech that results from brain damage.

People with FAS also show wide variability in their ability to pronounce sounds, choose words, or stress the right syllables. The accent can be strong or mild. Different listeners may hear different accents from the speaker with FAS (Lockett has said people have asked her if she's Polish, Russian, or French).

According to Miller and Ryalls, few studies have been published about speech therapy for treating FAS, and there's no real evidence that speech therapy makes a difference for people with the syndrome. More research is needed to determine if advanced techniques like electromagnetic articulography—visual feedback showing tiny movements of the tongue—could help those with FAS regain their original speaking manner.

Today, one of the pressing questions for neurologists is understanding how the brain recovers after injury. For that purpose, Miller and Ryalls write that "FAS offers a fascinating and potentially fruitful forum for gaining greater insights into understanding the human brain and the speech processes that define our species."

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

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