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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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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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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Climate change isn’t just raising the temperature of the world’s oceans — it’s also changing their color. As the oceans absorb the excess heat generated by greenhouse gases, that heat is altering the aquatic life in their waters. New research published in Nature in 2023 shows that the familiar blue hue of the oceans has been steadily transforming over the past 20 years into a greener shade, especially in tropical and subtropical areas of the world. 

The world’s largest migration happens in the ocean every single day.

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Every night, trillions of sea creatures called zooplankton travel to the ocean’s surface to feed on photosynthesizing phytoplankton. Although the distance for some organisms is only 1,000 feet, that’s the equivalent of a human swimming 50 miles in an hour.

The color of the ocean is dependent on a variety of factors, but one key is the light absorption of H2O. Water usually readily absorbs longer wavelengths of light — red, yellow, and green — and scatters blue. However, a concentration of marine life can cause emerald waters. The newly green hue detected by the 2023 research likely reflects a change in the ocean’s phytoplankton — the algae responsible for 70% of the world’s oxygen, and which also provides the foundation for the marine food web. Scientists monitored ocean color using NASA’s Aqua satellite, and found marked shifts toward green in about 56% of the world’s oceans between 2002 and 2022. Statistical simulations showed that added greenhouse gases are to blame, although it’s not exactly clear how, since areas that warmed the most at the surface weren’t the ones that turned green the most. Some scientists theorize that the change may have to do with reduced mixing in the layers of ocean water, caused by the heat, which limits the nutrients that rise to the surface and consequently affects the types of plankton that can survive. But don’t go color-correcting your photos just yet: While satellites can detect the change in ocean hue, the change is slight enough that most humans probably wouldn’t notice a difference.

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For those of us not blessed with a green thumb, it’d certainly be helpful if our plant friends could tell us when they need attention. Well, it turns out they do — we just can’t hear them. In early 2023, scientists from Tel Aviv University revealed the results of an investigation into whether plants make sounds in ultrasonic frequencies. Previous studies had established that plants can hear sounds, despite not having ears, so it seemed possible that they could create sounds without mouths. After isolating plants in a soundproofed acoustic chamber and a greenhouse and then recording them, the researchers were able to train a machine learning algorithm to differentiate sounds among three disparate plant states: unstressed, cut, or dehydrated. 

All types of tea are made from the same plant.

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Camellia sinensis is an evergreen shrub native to East Asia, whose leaves produce all types of tea. The differences among green, black, oolong, and white teas come from the ways they’re processed. Drinks like rooibos or herbal infusions are technically not tea, but tisanes.

Unstressed plants made little noise and continued along in their usual happy routine of photosynthesizing, but cut and dehydrated plants let out frequent small pops and clicks in a range too high for humans to hear. Stressed plants produced up to 40 of these clicks per hour, while dehydrated plants increased clicks as they got more and more parched. Although tomato and tobacco plants were originally tested, other crops were found to produce similar noises. It’s possible some animals that can hear in frequencies beyond human capabilities could respond to these noises. If a moth were trying to find a suitable plant to lay its eggs, for example, it might skip one that’s popping in distress. But big mysteries remain: For one thing, scientists don’t know how plants are making these sounds in the first place. All we know for sure is that the quiet lives of plants are not nearly as quiet as they seem.

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