The word “hippopotamus” means “river horse” in Greek, which makes sense given the amount of time — about 16 hours a day — these massive creatures spend in the water. But as it turns out, hippos can’t actually swim or even float. Their dense bones and heavy bodies cause them to sink, and their short legs and broad structure aren’t built for moving through water as easily as other aquatic mammals. 

What they can do, thanks to that density, is stand sturdily on a waterbed’s floor and walk or bounce along the ground. With their eyes and nostrils located high on their heads, they can still see and breathe while almost completely submerged.

Dolphins can recognize themselves in the mirror.

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Dolphins recognize their own reflection as early as 7 months old, showing self awareness even earlier than human babies.

Although they prefer the shallower parts of lakes, rivers, and swamps — typically around 6 feet deep — they’ve been observed in waters as deep as 40 feet, which they can propel themselves above by leaping like porpoises off the bottom. Even when they sleep, they can hold their breath for only about five minutes before an automatic reflex ensures they rise to the surface for air so they can rest without drowning.

The water isn’t just a playground for these creatures — it’s vital to their survival. Staying submerged helps keep their sensitive skin cool and hydrated under the hot African sun. It isn’t until dusk that they emerge and spend the next eight hours or so on land, grazing on grasses, before returning to their aquatic refuge when the sun reappears.

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The first dinosaur fossil was discovered in 1677 — not that the man who came upon it realized the magnitude of his find. The English naturalist Robert Plot thought that his discovery had belonged to a giant human, and it wasn’t until 1824 that the geologist William Buckland identified the bone for what it was. It took an additional 18 years for Sir Richard Owen, the most famed paleontologist of his era, to coin the term “dinosauria” — deinos meaning “terrible” or “fearfully great” in Greek, and sauros meaning “lizard.” True lizards and dinosaurs diverged from one another 270 million years ago, but the name stuck nevertheless. 

Land-dwelling dinosaurs and humans lived on Earth at the same time.

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Despite what “The Flintstones” led us to believe, humans never shared the planet with velociraptors, triceratops, or other non-avian dinosaurs. Early human ancestors first appeared in Africa some 6 million years ago, or 60 million years after the dinosaurs’ reign ended.

Suffice to say that the schoolteacher who called a young Owen “impudent” would have been surprised by his lasting scientific contributions, which also include describing many new species and founding London’s Natural History Museum. Owen later went on to feud with none other than Charles Darwin over their respective views on evolution. Owen developed his own influential theory of how animals developed, and disagreed with how Darwin interpreted it in On the Origin of Species — as well as with Darwin’s entire concept of natural selection. As a result, Owen’s scientific reputation has suffered, but we can still thank him for every 7-year-old’s favorite word.

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Anyone who’s ever serenaded their sweetheart has more in common with bats than they might think. In 2009, researchers at the University of Texas at Austin and Texas A&M studied the vocalizations of Tadarida brasiliensis — the Brazilian free-tailed bat, more commonly known as the Mexican free-tailed bat — and found the tunes to be surprisingly nuanced love songs. Though difficult for humans to hear, the songs consist of unique syllables that combine to form three types of “phrases”: chirps, buzzes, and trills. The males combine these phrases in different ways to attract females — and to warn other males to stay away.

Bats are blind.

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Despite the expression, bats can see just fine. While it’s true that most species use echolocation to hunt in the dark and thus rely more on sound than sight, some fruit bats don’t echolocate at all and certain species can even see UV light.

What makes this especially remarkable is that, until recently, bats weren’t thought to communicate with one another in such a structured way. But when the researchers listened to recordings of two free-tailed colonies in Austin and College Station, Texas, they discovered that they “use the same ‘words’ in their love phrases,” according to lead researcher Kirsten Bohn. And we’re learning more about bat communication all the time — in August 2021, researchers found that baby bats “babble” much like human infants do, practicing syllables over and over until they learn to get it right.

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When people draw clouds, the results are usually big, fluffy, white creations, known scientifically as cumulus clouds. Although there are dozens of different cloud types, this is the one we most often associate with the word “cloud.” Though they may not be as mesmerizing as lenticular clouds hovering over volcanoes or as puzzling as arcus clouds stretching for miles, there still are some facets of them that truly boggle the mind. Take, for instance, the weight of an average cumulus cloud. Although these collections of water vapor seem to float effortlessly, clouds are extremely heavy. In fact, according to the United States Geological Survey, the average cumulus cloud weighs 1.1 million pounds. 

A green cloud means a tornado is imminent.

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A green sky is caused by massive storm clouds filled with rain droplets that shift the color spectrum of the sky to green. Although a green sky means a nasty storm is likely on its way — one that could produce a tornado — it doesn’t mean that a destructive twister is all but certain.

If a cloud floats, how do you weigh it? Well, the U.S. National Center for Atmospheric Research estimates that the average cumulus cloud is about 1 kilometer (0.62 miles) long and 1 kilometer tall, or a billion cubic meters in volume. Meanwhile, the water density of a typical cumulus cloud is 0.5 grams (about a marble’s worth) per cubic meter. That means the average cumulus cloud holds 500,000,000 grams of water — or 1.1 million pounds. But while we have the equivalent of 100 elephants floating above our heads, the dryer, denser air beneath the cloud is even heavier, which is why those clouds can harmlessly float on by.

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Despite being thinner than human hair and lighter than cotton, spider silk is stronger than steel — and it isn’t even close. According to Science magazine, the insect-trapping, egg-protecting material is a full five times stronger than steel of the same diameter. It’s also highly elastic and can hold its strength at extreme temperatures, making it one of the most versatile substances in the world.

Spiders are insects.

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Along with such creepy-crawlies as scorpions and mites, spiders belong to the Arachnida class and are thus arachnids, not insects. The main difference? Most adult arachnids have eight legs rather than six and don’t have wings or antennae.

Only about half of all spiders spin webs, but all of them produce silk — which is as lucky for us as it is for them, considering how many uses it has. Ancient Greek soldiers used cobwebs to reduce bleeding, and it’s even been used in body armor developed for the U.S. military. So the next time you get scared after seeing a spider, just think: Its silk may one day save a life.

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