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Why Do Alligators Fall Asleep if You Rub Their Bellies?

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Myth has it that you can disarm an alligator by rubbing its belly. Some people don’t necessarily focus on the logistics of getting that close to the creature (let’s keep in mind the stomach is awfully close to all of those sharp teeth). However, we’re here to tell you that, yes, this is technically true—and alligators aren’t the only animals associated with this behavior.

"Belly rubbing refers to tonic immobility," the National's Zoo's Sean Henderson told The Washington Post in 2008. "It's a state of hypnotism generated by flipping the animal on its back and fully extending its neck" and, as we mentioned, stroking its belly. Fair warning, Henderson added: "Tonic immobility is generally brought about in an animal that is under heavily stressful conditions. Don't try this at home!"

According to Isaac Marks’s Fears, Phobias and Rituals: Panic, Anxiety, and Their Disorders, tonic immobility refers to the “prolonged stillness and decreased responsivity in a previously active animal in the face of threatening stimulation.” This state can last anywhere from 15 seconds to several hours, although the average length falls around eight to 10 minutes in chickens. (Yep, they can be affected too!)

Sharks are another type of creature susceptible to tonic immobility. There seem to be two different ways to trigger this effect in sharks, the most effective way being by rubbing a shark’s nose. While the exact reason why this works is unknown, one ecologist writes “[an] untested possibility is that a shark’s electroreceptors are concentrated in the snout area, and perhaps overstimulating this area ‘shocks’ them into immobility.”

Another means of immobilizing a shark is to invert it, flipping it on its back. WIRED recounted an especially odd occurrence of a shark being put into a state of tonic immobility—by another animal:

“In 1997, eyewitnesses watched a female orca off the coast of California seemingly induce tonic immobility purposely in a great white shark. The orca held the shark upside down, inducing tonic immobility, and kept the shark still for 15 minutes, which caused it to suffocate to death.”

Remember when we mentioned that tonic immobility occurs in chickens, too? WIRED theorizes that it’s a defense mechanism for the birds. “You can lay it on its side, tuck its head under its wing and gently rock it, or put it on its back and stroke its sternum,” the site reports. “You can wave your finger in front of its face—starting with your finger close to its beak and then pulling your finger slowly straight back. The chicken will focus on your finger.”

Tonic immobility affects different animals in different ways. "I've observed alpacas and llamas 'calmed' into a state of relaxation by gently rubbing the upper gum just beneath the cleft in the upper lip,” veterinary surgeon David Anderson told the Cincinnati Enquirer. “The animals stop resisting being held, and stop vocalizing.”

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 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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Animals
10 Notable Gestation Periods in the Animal Kingdom
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The gestation periods of the animal kingdom are varied and fascinating. Some clock in at just a few weeks, making any human green with envy, while others can last more than a year. Here are 10 notable gestation times for animals around the globe. The lesson? Be thankful that you’re not a pregnant elephant.

1. ELEPHANTS: 640-660 DAYS

Elephants are pregnant for a long time. Like really, really long. At an average of 95 weeks, the gestation period is more than double the length of a human pregnancy, so it shouldn't come as a shock that female elephants don't often have more than four offspring during their lifetimes. Who has the time?

2. HIPPOS: 8 MONTHS

A photo of a mother hippo and her baby in Uganda

Yes, it takes less time to make a hippopotamus than it takes to make a human.

3. GIRAFFE: 14-15 MONTHS

Baby giraffes can weigh more than 150 pounds and can be around 6 feet tall. Another fascinating tidbit: giraffes give birth standing up, so it's pretty normal for a baby to fall 6 feet to the ground.

4. KILLER WHALE: 17 MONTHS

There’s a reason for the long wait: after that 17 months, Baby Shamu emerges weighing anywhere from 265 to 353 pounds and measuring about 8.5 feet long. Yikes.

5. OPOSSUM: 12-13 DAYS

A baby opossum wrapped up in a blanket

Blink and you'll miss it: This is the shortest gestation period of any mammal in North America. But since the lifespan of an opossum is only two to four years, it makes sense.

6. GERBILS: 25 DAYS

Hey, they get off pretty easy.

7. GORILLAS: 8.5 MONTHS

It's not a huge surprise that their gestational periods are pretty similar to ours, right?

8. BLACK BEAR: 220 DAYS

A pair of black bear cubs

Also less than a human. Interestingly, cubs might only be 6 to 8 inches in length at birth and are completely hairless. 

9. PORCUPINE: 112 DAYS

This is the longest gestation period of any rodent. Thankfully for the mother, porcupine babies (a.k.a. porcupettes) are actually born with soft quills, and it's not until after birth that they harden up.

10. WALRUS: 15 MONTHS

Baby walruses? Kind of adorable. They certainly take their sweet time coming out, though.

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