Imagine this: You’re at the doctor’s office, and instead of one quick tap with the reflex hammer—the kind that makes your leg kick out without you meaning to—they just…keep going. Tap, tap, tap, right on that same spot below your knee, for a solid two minutes straight. It wouldn’t hurt you. But after a while, you’d probably start feeling pretty strongly about wanting it to stop—and if they didn’t, you might start wanting to kick someone on purpose. 

Now imagine you’re a dog, and someone finds your “sweet spot”—that one particular patch of skin on the side or back—and won’t quit scratching it. Suddenly, your back leg is kicking without your permission, over and over, like it’s got somewhere better to be. As adorable as it looks from the outside, it’s probably not exactly a party for you.

“It’s an annoyance,” says Nancy Thomas, DVM, a veterinarian with Telavets, an online veterinary expert consultation service. “It doesn’t do any good to continue doing it. The spinal cord is trying to say ‘get off of me.’”

So what is the mechanism behind your pup’s leg acting on autopilot?

Your dog’s leg has a mind of its own 

So it might look like your dog is practicing to bend it like Beckham, or maybe is angling for a spot with the Rockettes, but what is really happening is entirely out of your pet’s control. It’s something called the pruritic scratch reflex. 

It’s a reflex arc, a shortcut in the nervous system that bypasses the brain altogether to allow for an instant response. When something (your hand, a flea, a burr caught in the fur) touches the skin in that spot, sensory nerves pick up on it and send a signal straight to the spinal cord. The spinal cord doesn’t pause to think it over, according to Thomas; it’s the same shortcut your body uses when you touch a hot stove, although your dog’s involuntary kicks do not involve pain.

“You touch a stove, and the signal goes from the sensory nerves up to the spinal cord, and the spinal cord immediately sends a message back to your finger to get off the stove,” Thomas says. “It’s a millisecond kind of a deal.”

The reason dogs have the pruritic scratch reflex basically comes down to pest control: that particular area along your dog’s flank is prime real estate for fleas, ticks, mites, and burrs—the kind of small, easy-to-miss irritants that can burrow in or bite before a dog even notices. Rather than relying on conscious awareness to catch the pest, dogs’ built in a shortcut: If something touches down in that zone, the leg kicks automatically on the off chance it’s actually a threat trying to dig in. 

It’s the same basic reflex that makes a horse’s skin twitch to shake off a fly, says Thomas, who also created an emergency medical ID tag for horses and their riders.

“It’s a mechanism designed to keep nefarious things off the body,” Thomas says.

It’s not the same as tickling

A very common misunderstanding around the pruritic scratch response is that it is a form of tickling, and it’s easy to see why: your dog is responding in a riotous, involuntary, and rather comical way to a physical trigger. 

But as gleeful as it looks when your dog breaks into those rapid-fire leg kicks, the experience is probably neutral at best for your dog. By continuing to do it, you could be “perpetuating the annoyance,” according to Thomas. Even tickling isn’t universally and unequivocally loved.

“A lot of people hate being tickled,” she says. 

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A scratch your dog will actually enjoy

To be clear, this doesn’t mean your dog is necessarily having a miserable time every time you find that spot. In general, the reflexive leg kick is just proof that your dog’s built-in protective wiring is working exactly the way it’s supposed to. But there’s one pattern worth keeping an eye on. If your dog reacts almost anywhere you touch them, or seems unusually sensitive even on their belly (which is normally a calmer, less reactive area due to its lack of contact with the ground), that’s worth mentioning to your vet. 

“That’s a possible red flag for atopy,” Thomas says, referring to allergies or skin inflammation that leaves the whole body more sensitive. It’s similar to how a patch of poison ivy makes even light touch uncomfortable.

“That might be a bit of a sign,” Thomas says. “These dogs might be a little extra sensitive, due to a skin condition.”

To make bonding with your dog more enjoyable for both of you, Thomas advises sticking to areas not commonly associated with the pruritic scratch reflex, such as the belly. She also recommends watching your dog’s body language to ensure they’re having as much fun as you. It’s a much better way to ‘get your kicks’ without turning your dog into a full-on kickboxer. 

“If you’re rubbing their belly, and they’re all spread out and relaxed-looking, that’s a sign you’re on the right track,” she says. 

In Ask Us Anything, Popular Science answers your most outlandish, mind-burning questions, from the everyday things you’ve always wondered to the bizarre things you never thought to ask. Have something you’ve always wanted to know? Ask us.

The post Why do dogs’ legs shake during pets? It’s not because they like it. appeared first on Popular Science.

Growing up, many of us remember dutifully taking a few more bites of protein (and, of course, vegetables) to appease our moms before we were allowed to progress to the sweet, carb-heavy goodness of dessert. Lately, it seems hard to say whether our moms would be delighted or horrified to see what has happened to protein since.

Just walk into any grocery store right now, and protein is everywhere. Protein water. Protein chips. You can even request protein foam on your favorite fancy latte. Somewhere, a bodybuilder is chugging a protein shake the size of a fire extinguisher as you read this. It’s safe to say this is not your mother’s protein.

To be fair, protein deserves at least some of its mom-and-jock-endorsed reputation. It helps build muscles, keeps you feeling full, and is an essential nutrient we truly can’t live without. Older adults, especially, have been told to eat more of it as they age. 

So, is more protein always better? According to a large review of several recent studies, the answer may be no.

“We think of protein as beneficial,” Dr. Dudley Lamming, a professor at the University of Wisconsin-Madison and lead researcher of the review, told Popular Science, “but a number of studies have started to come out showing that when you look at large populations over the course of decades, people who were eating more protein over the course of these decades were having higher rates of age-related diseases.”

A pattern in the data sparked new questions 

Lamming didn’t set out looking for a problem with protein. If anything, he was surprised by a contradiction he was noticing between population data and the conventional wisdom about protein—people who ate more protein over time were showing higher rates of cancer, diabetes, and cardiovascular disease. 

“The question is, how can this be?” he remembers wondering.

Lamming’s review looked at more than 350 studies in total, most of which were conducted in mice and other lab models, examining things like lifespan, metabolic health, and cellular aging. 

But a smaller slice, about five or six randomized trials, tested protein restriction directly in people. Those human trials showed consistent short-term benefits: People lost weight, their fat mass declined, and in one study of people with type 2 diabetes, insulin sensitivity improved.

Lamming adds that these results do not appear to be associated with mere calorie reduction.

“In fact, because dietary protein is satiating, people in our studies and others actually ate more calories when they were on a protein-restricted diet,” he says. “But they lost weight, and that’s because energy expenditure increases.”

One hormone may explain what’s happening

To understand the potential connection between protein restriction and increased energy expenditure, Lamming’s review explored existing mouse studies on the topic. Findings from these studies indicate that when protein intake drops, the liver releases a hormone called FGF21. That hormone signals the brain, which in turn triggers what researchers call “beiging.”

“This is a process that essentially tells your fat tissue to stop simply storing fat, but actually to start metabolizing it and burning it for energy,” says Lamming. 

In practice, protein restriction doesn’t mean cutting protein out altogether. Most people get about 16 to 17 percent of their calories from protein; in the studies Lamming and his team reviewed, that’s typically cut by around half, down to roughly seven to nine percent.

“We’re not talking about restricting to an unhealthy level where you’re protein insufficient,” he says. “What we’re really talking about, in most cases, is restricting down to the recommended daily allowance as reported by the World Health Organization, which is about 0.8 grams per kilogram [of body weight].” 

So the average man (weighing an average of about 200 pounds) would need about 73 grams of protein a day. The average woman, on the other hand, (weighing about 170 pounds) would need 62 grams of protein a day. For reference, a small three ounce filet of salmon contains about 24 grams of protein.

You don’t necessarily have to restrict protein as a whole to achieve these benefits, either; mouse studies found that cutting back on specific amino acids, including methionine, isoleucine, and valine, may provide some of the same benefits in terms of fat mass, blood sugar control, and longevity. 

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Exercise may change the equation

This doesn’t necessarily mean everyone should be in a hurry to throw away their protein waffles. Lamming is careful to note that people who exercise routinely may be an exception.

“We actually think that dietary protein has negative metabolic health outcomes for sedentary people, like the general population, since most of the population is fairly sedentary,” he says. “But maybe people who are exercising need more protein to help build muscle, and maybe it wouldn’t have these negative metabolic outcomes.”

Although these findings are based only on mouse studies so far, they may suggest that working out might protect against the downsides of higher protein intake, Lamming says. 

“Fortunately,” he says, “a lot of the people who are very pro-protein are also people who are exercising.”

Lamming says his team plans to test these ideas—specifically, whether protein supplementation genuinely benefits those who exercise, and whether restriction benefits those who don’t—more directly in both mice and people over the next few years.

“For your typical person who’s not engaged in exercise, we would suspect, based on our research, that eating more calories in the form of protein would be detrimental,” he says. 

Lamming’s own suggestion for sedentary people: Consider skipping the protein-added version of a product when a regular option is available.

He was quick to add, however, that those who can safely exercise certainly should.

“No one’s going to argue that more exercise would be bad,” he says.

In Ask Us Anything, Popular Science answers your most outlandish, mind-burning questions, from the everyday things you’ve always wondered to the bizarre things you never thought to ask. Have something you’ve always wanted to know? Ask us.

The post You might be eating too much protein appeared first on Popular Science.

Imagine this: A giant sperm whale (Physeter macrocephalus) has just swallowed you whole.

It might seem like a bizarre scenario to envision, but you’d hardly be the first. In the Bible’s Book of Jonah, the belly of a whale is the setting for the prophet Jonah’s  three days of repentance and prayer. In the 1940 Disney film Pinocchio, Geppetto manages to rig up a cozy living space inside the stomach of Monstro the sperm whale, complete with amenities including  a small fire and a fishing setup for seafood that drifts in. Even his pet goldfish, Cleo, is swimming inside the microcosm of her highly ironic fishbowl.

Surviving inside of a giant sea creature has become a classic “fish tale” of human resilience and redemption. In the latest reimagining of this theme, the upcoming movie Whalefall, a scuba diver is swallowed by a sperm whale and has exactly one hour to escape before his oxygen runs out.

But for all our fascination with extended whale-squatting, one fact remains: it has never actually happened. The few close calls with whale ingestion have involved humpback whales, a species physically incapable of swallowing a person. In all cases, the whale spat the person up as quickly as you might cough up a bug that flew into your mouth.

“I wouldn’t call that swallowed,” Shane Gero, a whale biologist and Lead Biologist at Project CETI, tells Popular Science. “I would call that a mistake by both the mammals involved.”

So, if it’s never actually happened, is it even possible?

A highly unlikely accident 

Whalefall is the film adaptation of a 2023 novel of the same name by Pulitzer Prize winning author Daniel Kraus, and arrives in theaters on October 16.Protagonist Jay Gardiner is on a diving expedition to find the remains of his late father, a mariner who died at sea. Suddenly, Jay is swallowed by a giant sperm whale, with only an hour of oxygen remaining in his scuba tank. To try and survive, Jay deploys a series of highly resourceful, increasingly MacGyver-esque maneuvers, including using the beak of a squid to cut through the whale’s stomach lining, and navigating his climb up into the whale’s throat using the glow of a jellyfish. 

The ordeal is an adrenaline-fueled adventure for Jay, but could any of it ever happen? Gero, who has studied sperm whales for over 20 years, thinks it’s highly improbable, starting with the swallowing part.

“To my knowledge, no one has ever been eaten by a sperm whale,” he says.

Gero hypothesizes that after some generous suspension of disbelief about sperm whales’ feeding habits and anatomy, there could be a situation where “the largest sperm whale ever” could accidentally ingest a human.

“I think anatomically, maybe you could shove a slender human down the throat of a very large, male sperm whale,” he says. “Would it happen? Very unlikely. Certainly not with scuba gear and a scuba tank making the human that much bigger.”

Yet Gero, who has read the novel, praised the book’s meticulous efforts to make the science line up, including its explanation for why a sperm whale would be anywhere near a scuba diver. Sperm whales usually feed at about 3,000-feet-deep at the bottom of the ocean, an area not typically occupied by scuba divers. The book reconciles this by having a giant squid (Architeuthis dux) struggling at the surface to escape being eaten by the sperm whale. When the whale comes to the surface to eat the squid, the squid latches onto Jay, who is then pulled into the whale’s mouth. But even after accepting this explanation, Gero notes that sperm whales use echolocation, which would likely distinguish a human as unusual prey, not a potentially tasty morsel.

“Eating a human by accident seems very unlikely, but it makes for a really exciting story,” Gero says.

The odds of surviving inside a whale

If a person somehow managed to survive entering the mouth of a sperm whale without drowning from the propulsive rush of water, Gero says that their luck would worsen almost immediately.

“More than likely, the human drowns the second they get smashed into the mouth of the whale, whether they were drawn in by a squid or accidentally brought into the mouth of a whale,” he says. “My guess is the person dies the second they enter the mouth.”

Gero raises another interesting possibility. Sperm whales usually prey on boneless squid, so consuming a scuba-outfitted human could be a choking hazard, and could choke to death. 

This would certainly make for a shorter movie, but Gero notes that the whale’s body could also have a more lively response to an unwanted foreign object in its mouth.

“When I swallow something that I shouldn’t have, it’s like a non-controllable response — your body just starts moving its mouth and coughing,” Gero says. “In that sort of movement, or freakout, it probably is going to do a lot of physical damage to the human.”

Although Gero acknowledges that he is not a  whale anatomist, he still believes that it would be highly unlikely for any living creature to make it into the stomach of a sperm whale, let alone set up camp there.

“There are acids and gases,” he says. “The digestive tract of any mammal is not meant to be a livable place for any prey that ends up there.”

Dr. Joy Reidenberg, a comparative anatomist at the Icahn School of Medicine at Mount Sinai in New York City who consulted on the anatomy for both the Whalefall book and film, explains that a sperm whale’s stomach is divided into four chambers. These chambers are a vestige from their early days as a land-based, plant-eating mammal about 50 million years ago. The first chamber is lined with thick, muscular tissue. It’s responsible for mashing up food, since sperm whales’ teeth, found only on the lower jaw, are too pointed to chew.

If Jay needed something solid to grab onto and pull himself toward the whale’s throat, Reidenberg tells Popular Science he wouldn’t find much. It would mostly be “wet, slimy, squishy walls,” with “no hooks, no handles.” The one exception is the whale’s voice box, or larynx, which sticks up like a rigid pipe. 

“If he gets his arm around that, he can pull himself out,” she explains.

Even in that situation, Reidenberg says, few people would live to tell this phenomenal tale.

“Most people, unless they have protection and air, couldn’t survive this situation. Also, a sperm whale would probably never swallow a person.”

Meet your actual nightmare 

While the  fictitious scenario of a massive sperm whale swallowing a human relies as much on poetic license as it does grounded science, could any other land or sea animal engulf an entire human being?

Horrifyingly, yes. The reticulated python (Malayopython reticulatus), which is the world’s longest snake species and can measure as much as  26-feet-long, has been known to take in an entire human. According to a 2025 study tracking python-related deaths in Indonesia, 17 people were preyed upon by reticulated pythons between 1927 and 2025. Astonishingly, four of these people survived, although it’s unlikely they spent any quality time inside the snake. In several of the fatal cases, the humans were swallowed whole.

Gero notes that a green anaconda (Eunectes murinus) might also be up to the task, since they can swallow animals as large as deer. Even then, this prey is already dead when it’s consumed.

“Anacondas famously wrap around and crush their prey,” Gero says. “The body is limp by the time it goes down.”

Why these fish tales endure

Gero also makes one key distinction about sperm whales: they have absolutely no interest in preying on humans, intentionally or otherwise. In fact, humans have spent centuries slaughtering whales for oil, an uneasy relationship that may be part of why they loom so large in our storytelling.

“If those stories exist from the whaling days, they’re more a lesson to future whalers than they are based in reality,” he says. “I’ve never seen any kind of aggression from a sperm whale. These are gentle giants of the deep.”

Gero hopes movies like Whalefall will spark genuine curiosity about the intelligent, peaceful animals behind the myth. He and the team at Project CETI are working to decipher how sperm whales communicate with each other. In the meantime, you can visit listen.projectceti.org to record what you’d say to a sperm whale, if you ever had a chance. 

This story is part of Popular Science’s Ask Us Anything series, where we answer your most outlandish, mind-burning questions, from the ordinary to the off-the-wall. Have something you’ve always wanted to know? Ask us.

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The post Could a whale really swallow a human? We asked a biologist. appeared first on Popular Science.