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The Mystery of the Sloth Poop

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Three-toed sloths are just that: three-toed, and slothful. They live high in the tree canopy and feed exclusively on the foliage there, hanging around most of the time and moving slowly when they move at all. 

They only descend from their leafy home once a week to make a bathroom run. After shimmying down the trunk of a tree, a sloth digs a small hole in the dirt, poops in it, covers their makeshift toilet with leaves, and then climbs back up. This is not the most efficient way to poop, nor the safest. Climbing down a tree to ground level and then back can cost a sloth as much as 8 percent of its daily calorie intake, and the animals are out of their element and incredibly vulnerable on the ground—more than half of all recorded sloth deaths are caused by attacks from predators at or near the ground. 

If a simple poop can cost a sloth its life, why do it like that? The three-toed sloth’s cousin, the two-toed sloth, simply defecates from the canopy. It can’t be pleasant to be standing underneath one when that happens, but the sloths are safer for it. If three-toed sloths keep making these costly and risky trips to a ground-floor bathroom, there must be something that makes the trip worth it. 

Scientists have come up with a few possible benefits for ground-pooping, like fertilizing the trees that the sloths call home or revealing their locations to other sloths so they can mate (how romantic). Ecologist Jonathan Pauli and other researchers from Wisconsin and Virginia have a different idea, though, that’s rooted in the sloth’s dietary problems. 

Sloths are among the 0.02 percent of mammals that are specialized arboreal herbivores, living in trees and foraging for food there. This lifestyle isn’t an easy one. To live on a tree branch, you have to be relatively small and light, but a limit on body size also puts a limit on how much you can digest. A sloth’s main source of food, leaves, is pretty nutrient-poor and not easy to digest to begin with, so they’re under some serious nutritional constraints. Pauli and his team wondered if, when sloths went downstairs to use the bathroom, they were also grabbing some extra food. 

The key here is the miniature zoo that sloths carry around with them. Their thick fur is home to all kinds of algae, fungi, arachnids and insects. Among these tenants are moths from the genus Cryptoses, commonly (and adorably) called “sloth moths.” These moths are absolutely dependent on their host sloth’s weekly bathroom trip. The females lay their eggs in the sloth dung, which the larva then live off of until they become adults and can fly upward to move onto their own sloth. Maybe the sloths are just as dependent on the moths, and aid their lifecycle because the bugs are somehow nutritionally important. 

The researchers took locks of hair from the ground-pooping brown-throated three-toed sloth and from Hoffmann’s two-toed sloth, which prefers a “bombs away” style of defecation. After removing and counting the moths from each hair sample, they looked at the nutrients available in the hair and then compared them to some sloth stomach contents to see if there was any connection between the moths, the contents of the hair, and what the sloth had been eating.

They found that sloths that had more moths on them also had more nitrogen-rich hair and more algae growth. The algae also turned up in the sloths’ stomachs, and when the researchers analyzed it they found that it was easily digestible and rich in carbs, proteins, and fats. 

So the perilous pooping process keeps the moths around. Moths mean more nitrogen (why, exactly, is still an open question—the moths might be dragging the nitrogen up from the sloth poop or releasing it when they die). More nitrogen promotes more algae. And algae seems to be a good nutritional supplement—though the researchers haven’t crunched the numbers to see just how much energy and nutrients the algae could provide. It’s a roundabout way to get a meal, but whatever works. Two-toed sloths, by the way, are less fussy eaters, and will forage a wider area, which may explain why they can poop from the canopy—they don’t need the moths or the algae that comes with them. 

There’s one big problem with all of this, according to other sloth researchers: There’s little evidence that the sloths are eating the algae from their hair. No one has seen them licking their fur or pawing at it in a way that suggests they’re picking the algae out for a snack. The study found bits of algae in sloth stomachs, but no one’s even sure if it's enough make any real nutritional impact. 

Becky Cliffe, a zoologist working at the Sloth Sanctuary of Costa Rica, doesn’t think the algal snacks are worth the risk of a climb down a tree, because sloths can get along fine without them. “For a start, sloths in captivity that are fed a natural diet but don’t have any algae are perfectly healthy,” she writes. “Blood analysis done at the Sloth Sanctuary shows no difference between these captive animals and their wild, algae-covered counterparts.”

Even if the sloths are chowing down on algae when no one is looking, it doesn’t seem to be so integral to their diet that they’d risk time on the ground. For now, the way a sloth poops remains one of the great mysteries of the rainforest. 

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iStock // Ekaterina Minaeva
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Man Buys Two Metric Tons of LEGO Bricks; Sorts Them Via Machine Learning
May 21, 2017
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iStock // Ekaterina Minaeva

Jacques Mattheij made a small, but awesome, mistake. He went on eBay one evening and bid on a bunch of bulk LEGO brick auctions, then went to sleep. Upon waking, he discovered that he was the high bidder on many, and was now the proud owner of two tons of LEGO bricks. (This is about 4400 pounds.) He wrote, "[L]esson 1: if you win almost all bids you are bidding too high."

Mattheij had noticed that bulk, unsorted bricks sell for something like €10/kilogram, whereas sets are roughly €40/kg and rare parts go for up to €100/kg. Much of the value of the bricks is in their sorting. If he could reduce the entropy of these bins of unsorted bricks, he could make a tidy profit. While many people do this work by hand, the problem is enormous—just the kind of challenge for a computer. Mattheij writes:

There are 38000+ shapes and there are 100+ possible shades of color (you can roughly tell how old someone is by asking them what lego colors they remember from their youth).

In the following months, Mattheij built a proof-of-concept sorting system using, of course, LEGO. He broke the problem down into a series of sub-problems (including "feeding LEGO reliably from a hopper is surprisingly hard," one of those facts of nature that will stymie even the best system design). After tinkering with the prototype at length, he expanded the system to a surprisingly complex system of conveyer belts (powered by a home treadmill), various pieces of cabinetry, and "copious quantities of crazy glue."

Here's a video showing the current system running at low speed:

The key part of the system was running the bricks past a camera paired with a computer running a neural net-based image classifier. That allows the computer (when sufficiently trained on brick images) to recognize bricks and thus categorize them by color, shape, or other parameters. Remember that as bricks pass by, they can be in any orientation, can be dirty, can even be stuck to other pieces. So having a flexible software system is key to recognizing—in a fraction of a second—what a given brick is, in order to sort it out. When a match is found, a jet of compressed air pops the piece off the conveyer belt and into a waiting bin.

After much experimentation, Mattheij rewrote the software (several times in fact) to accomplish a variety of basic tasks. At its core, the system takes images from a webcam and feeds them to a neural network to do the classification. Of course, the neural net needs to be "trained" by showing it lots of images, and telling it what those images represent. Mattheij's breakthrough was allowing the machine to effectively train itself, with guidance: Running pieces through allows the system to take its own photos, make a guess, and build on that guess. As long as Mattheij corrects the incorrect guesses, he ends up with a decent (and self-reinforcing) corpus of training data. As the machine continues running, it can rack up more training, allowing it to recognize a broad variety of pieces on the fly.

Here's another video, focusing on how the pieces move on conveyer belts (running at slow speed so puny humans can follow). You can also see the air jets in action:

In an email interview, Mattheij told Mental Floss that the system currently sorts LEGO bricks into more than 50 categories. It can also be run in a color-sorting mode to bin the parts across 12 color groups. (Thus at present you'd likely do a two-pass sort on the bricks: once for shape, then a separate pass for color.) He continues to refine the system, with a focus on making its recognition abilities faster. At some point down the line, he plans to make the software portion open source. You're on your own as far as building conveyer belts, bins, and so forth.

Check out Mattheij's writeup in two parts for more information. It starts with an overview of the story, followed up with a deep dive on the software. He's also tweeting about the project (among other things). And if you look around a bit, you'll find bulk LEGO brick auctions online—it's definitely a thing!

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Nick Briggs/Comic Relief
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What Happened to Jamie and Aurelia From Love Actually?
May 26, 2017
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Nick Briggs/Comic Relief

Fans of the romantic-comedy Love Actually recently got a bonus reunion in the form of Red Nose Day Actually, a short charity special that gave audiences a peek at where their favorite characters ended up almost 15 years later.

One of the most improbable pairings from the original film was between Jamie (Colin Firth) and Aurelia (Lúcia Moniz), who fell in love despite almost no shared vocabulary. Jamie is English, and Aurelia is Portuguese, and they know just enough of each other’s native tongues for Jamie to propose and Aurelia to accept.

A decade and a half on, they have both improved their knowledge of each other’s languages—if not perfectly, in Jamie’s case. But apparently, their love is much stronger than his grasp on Portuguese grammar, because they’ve got three bilingual kids and another on the way. (And still enjoy having important romantic moments in the car.)

In 2015, Love Actually script editor Emma Freud revealed via Twitter what happened between Karen and Harry (Emma Thompson and Alan Rickman, who passed away last year). Most of the other couples get happy endings in the short—even if Hugh Grant's character hasn't gotten any better at dancing.

[h/t TV Guide]

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