Sloths seem to be everyone's "spirit animal." They get to eat, sleep, and hang out in trees all day, going about their business without a care in the world. Or at least that's how it looks. As it turns out, there are plenty of good reasons why sloths are so sluggish—and laziness isn't one of them. Here are 13 things you should know about the world's slowest animal.

1. TWO-TOED AND THREE-TOED SLOTHS AREN'T ALL THAT SIMILAR.

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The cute little babe pictured above is a two-toed sloth, of which there are two species belonging to the Megalonychidae family. The four species of three-toed sloths, on the other hand, are part of the Bradypodidae family. The two groups are only distant relatives and have a few notable differences between them. While three-toed sloths are active in the daytime, two-toed sloths are nocturnal creatures. Three-toed sloths are also smaller and slower than their two-toed counterparts.

2. BOTH HAVE THREE TOES, THOUGH.

The names used to distinguish the sloths are somewhat of a misnomer. Both have three toes on each hind limb. The real difference applies to the fingers on their forelimbs; one family has two claws, while the other has three. To avoid confusion, some groups—like The Sloth Conservation Foundation—have starting calling them two-fingered and three-fingered sloths.

3. THEY'RE RELATED TO THE EXTINCT GIANT GROUND SLOTH.

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Two-toed and three-toed sloths both evolved from giant ground sloths, the largest of which weighed several tons and stood about 12 feet tall. The animals went extinct about 10,000 years ago, likely due to hunting by early humans.

4. THEY WOULD FAIL AN EYE EXAM.

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Sloths aren't exactly known for their sharp senses, and this is especially true for their eyesight. A mama three-toed sloth can't spot her own baby from 5 feet away, and combative male sloths have been observed trying to hit each other from a similar distance. Scientists say a genetic mutation is to blame. Three-toed sloths are born without cone cells in their eyes, which are needed to detect colors. As a result, they see things in black and white, and in poorer resolution, too. They also have a hard time handling bright lights—not the best trait for a diurnal (daytime) creature to have.

5. THEY'RE SURPRISINGLY GOOD SWIMMERS.

Sloths are painfully sluggish on land. Their hind legs are weak, so they have to use their arms and upper body strength to pull themselves forward. Plop them in some water, though, and they can move three times as fast. Their long front arms make them skillful swimmers, and they can hold their breath underwater for up to 40 minutes. If a body of water is nearby, they may jump in and use it as a shortcut to navigate the forest more quickly. In the above clip narrated by David Attenborough, a male sloth swims as fast as he can—which is pretty fast, all things considered—to track down a female sloth's mating call.

6. THEIR "LAZINESS" IS A SURVIVAL TACTIC.

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It's no secret that sloths are slow. Their reaction time is about a quarter as fast as a human's, and they move at a pace of 6 to 8 feet per minute. Indeed, three-toed sloths are the slowest animals on Earth, beating out other famously slow animals like giant tortoises and snails. When the animals were first documented in 18th-century scientific texts, they were harshly described as "the lowest form of existence." But their slowness is why they haven't died out. Sloths largely subsist on leaves, and it can take up to a month for their four-part stomachs to digest a single meal. The leafy greens aren't very nutritious, so they have to conserve as much energy as possible to survive—and that means moving less. As a bonus, their slow movements help them go unnoticed by predators that rely on sight to hunt down prey, like jaguars, ocelots, and harpy eagles.

7. THEY DO JUST ABOUT EVERYTHING IN TREES …

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Sloths are arboreal creatures, so they spend almost all of their time in trees. They eat, sleep, mate, and give birth while hanging upside-down—a feat made possible by their anatomy. Their internal organs are anchored to their abdomen, which shifts weight away from their diaphragm and lets them breathe more easily, and therefore expend less energy.

Three-inch claws also help them latch onto branches and stay suspended far above the forest floor. In fact, their innate ability to cling to branches is so strong that dead sloths have been found dangling from trees, lending new meaning to the phrase "death grip."

8. … EXCEPT POOP.

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As a consequence of their slow metabolisms, sloths poop once a week—and sometimes just once a month. Two-toed sloths often let 'er rip from the trees, but three-toed sloths follow a bizarre routine that has baffled scientists. They typically make their way down to the forest floor to relieve their backed-up bowels, and once they get there, they do a little "poo dance" while digging a small hole to defecate inside. Without the camouflage afforded to them by the foliage of the forest canopy, sloths are much more likely to be picked off by predators. About half of all sloth fatalities occur when they're on the ground, most likely doing their business or finishing up. So why do they do it? It might have something to do with sex, and marking a tree for a potential mate to find. "Whatever is going on, it's got to be kind of life or death for survival," sloth biologist Rebecca Cliffe tells The Washington Post. "In my brain, that tells me that it's probably something to do with reproduction because that is the driving fact behind most animals' crazy behaviors."

9. AND THEIR POOPS ARE ENORMOUS.

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When they do poop, their turds tend to be massive. If you put the contents of a sloth's bowel movement on a scale, they might weigh up to one-third of the animal's body weight. This is 282 percent larger than what scientists would expect to see in an animal of the sloth's size. "You can watch their stomachs physically shrink as they poo," Cliffe tells The Washington Post. Oddly enough, though, sloths don't fart. So there's that.

10. ALGAE OFTEN GROWS ON THEIR FUR.

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Sloths have a symbiotic relationship with algae. Studies have shown that algae is sometimes passed down from a mother sloth to her baby, and the transfer is mutually beneficial for both animal and plant. The sloth's long fur creates a cozy home for the algae—which readily absorbs the water they need to thrive—and the sloths get a coat of green-tinted fur that doubles as camouflage. Sloths also eat the algae, which provides a much-needed source of nutrients.

11. FEMALE SLOTHS SCREAM WHEN THEY WANT TO MATE.

Females get the courting process started by letting out a loud, high-pitched scream to let male sloths know she's ready to mate. "This call is a loud 'eeeeeh' lasting more or less one second," sloth researcher Adriano Chiarello tells Live Science. Researchers are unsure on the particulars of sloth courting or copulation, or even if males will fight for the right mate with the screeching female (or if any fights are territorial instead). Whatever the details, the ensuing gestation period is between five and six months, and then the female sloth will birth one baby sloth, which is—uninterestingly—just called a baby sloth.

12. THREE-TOED SLOTHS CAN ROTATE THEIR HEADS 270 DEGREES.

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This special talent puts three-toed sloths in the same category as many owls. In both species, this Exorcist-esque ability can be attributed to their bone structure. Sloths have extra vertebrae at the base of their necks that let them look in all directions with ease. Although sloths aren't great at defending themselves, they can at least see when danger is approaching.

13. FOR SUCH DEFENSELESS CREATURES, THEY LIVE FAIRLY LONG LIVES.

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"Live slow, die whenever"—the unofficial slogan bestowed upon sloths by the internet—pretty much gets it right. On average, sloths live to be about 20 years old, but some species can live longer in captivity. The world's oldest sloth—a female of the Hoffman's two-toed variety named Miss C—died last year at the ripe old age of 43. She was a lifetime resident of Australia's Adelaide Zoo.