Snakes are often pictured curled around a tree in a dense jungle or hiding in a desert waiting to strike some unsuspecting prey. But they’re just as capable in the water as they are on land — in fact, all species of snakes can swim. In North America, a famous example is the cottonmouth (Agkistrodon piscivorus), named for the white color on its mouth that goes on full display when the creature is angry. This snake, native to the southeastern U.S., also goes by the name “water moccasin” because of its predilection for estuaries, bays, and rivers. 

All snakes lay eggs.

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Only about 70% of snakes are oviparous, meaning they lay eggs to produce young. The other 30% give birth, known as ovoviviparity, to snakes encased in an amniotic sac. This is especially true for snakes in cold climates, where eggs wouldn’t survive.

But even going a step beyond the familiar cottonmouth, some 60 species of marine snakes derived from the cobra family call the ocean their home, and monstrously large snakes such as anacondas also spend most of their life in the water. Even snakes that generally have no business in water, such as the desert-loving rattlesnake, can swim in a pinch. Members of the suborder Serpentes (to which all snakes belong) are such good swimmers because their elongated bodies can easily propel them through the water, and some have even evolved tails that look like paddles. But don’t worry, ophidiophobes: It’s not like the Earth’s waters are teeming with snakes. Snakes can’t live in areas that are too cold, and many spots — Alaska, New Zealand, and Ireland, to name a few — are entirely free of them. 

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While cats give off a solitary vibe — often appearing much more aloof than their canine counterparts — felines are actually very social creatures. They form bonds with littermates, establish colonies, and may develop just as strong a connection with their pet parents as dogs do. Maybe the lesser-known social nature of cats can begin to explain another fascinating finding: Cats are capable of up to 276 unique facial expressions. In 2021, researchers at UCLA recorded 194 minutes of cat-to-cat facial expressions at a nearby CatCafé Lounge. Then they coded all those facial muscle movements, excluding things like chewing and yawning, and discerned 276 unique expressions.

Purring means a cat is content.

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While cat purring can mean your favorite feline is feeling content, there’s a variety of other reasons for cats to rev their little engines, including when they’re hungry, injured, or frightened. A purr’s frequency has also been known to spur bone regeneration.

Each of these feline expressions included four of 26 unique facial movements — things like parted lips, jaw moves, and even pupil dilation. Humans, by comparison, have about 44 facial movements, which some estimates say translates into about 10,000 facial expressions. Although limited compared to humans, cats still have far more expressions than experts realized. As one veterinary behaviorist put it, “there is clearly a lot going on that we are not aware of.” Even after 10,000 years of domestication (and an even greater number of cat videos), the little lions in our living room still have the capacity to surprise. 

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Kangaroos are one of several biologically unique creatures endemic to Australia. One of their most unusual traits is that their long hind feet and muscular tails prevent them from being able to walk backward except with great difficulty. In fact, kangaroos can’t even really walk forward like other animals. Instead, they ambulate using a hopping motion called saltation in which their hind feet touch the ground synchronously instead of alternating one at a time. They also use their long tails to balance and propel themselves forward, almost like a third hind leg. This physiological composition makes it effectively impossible for kangaroos to walk or hop backward, as their tails are far too heavy and cumbersome to allow for easy reverse navigation. When they do want to move “backward,” they do so by turning around and facing that direction.

Kangaroos are only about an inch long when born.

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Baby kangaroos (joeys) are roughly an inch long when born. Immediately after birth, the baby crawls unassisted into the mother’s pouch, where it spends its first four months. After that the joey emerges for short periods of time to graze before leaving the pouch for good after about 10 months.

Much like their marsupial mates, emus, another endemic Australian creature, also struggle to walk backward. While these large, flightless birds are capable of sprinting at speeds of up to 31 mph, they can only do so facing forward. When they do move backward, they’re forced to do so very slowly. It’s believed that their knee joints, in addition to their long legs and unusual body shape, prevent them from moving quickly in reverse. Given this shared difficulty in backing up, it’s worth noting that both the kangaroo and the emu also share the distinction of appearing on Australia’s Commonwealth Coat of Arms. According to the country’s Department of the Prime Minister and Cabinet, the animals were chosen to symbolize a country that’s always moving forward rather than backward.

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Although not the most glamorous of methods, sweating is a biologically ingenious way to keep cool. Our sweat glands employ energy — in this case, heat — to evaporate water off our skin, which in turn cools us down. Humans, along with some monkeys and all of the great apes, use a similar cooling technique, but sweating isn’t as ubiquitous throughout the animal kingdom as you might expect. For example, pigs don’t sweat — not really, anyway. 

Sweat doesn’t smell.

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Sweat itself doesn’t smell — the liquid is made up of lots of water and a little salt. However, sweat glands in our armpits and groin release a type of sweat that is protein-rich, which bacteria then feeds on. The byproduct of this microscopic meal is what actually causes body odor.

Pigs do have some sweat glands, but they’re insufficient to play a significant role in regulating the creatures’ body temperatures. Instead, some of a pig’s internal body temperature is regulated by a thyroid-produced hormone, but the most fast-acting method for keeping cool is simply wallowing in mud. When the mud evaporates, it takes some heat with it, just as when human sweat evaporates. Pigs will also seek shaded areas, lie flat on cool ground, or even pant similarly to dogs. The fact that pigs don’t sweat (a lot) has created an inaccurate idea that eating a pig is unhealthy because they can’t release toxins through sweat — but that’s just a myth. 

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