Being a sloth isn’t all lazing around in trees and munching on leaves. Occasionally, the slow-moving animals have to make their way to the forest floor to do the one task no animal can escape: pooping. It’s a much more intense process than heading to the bathroom is for humans. And for a startling number of sloths, it turns deadly.

The sloth metabolism, like everything else about these odd rainforest animals, works very slowly. It can take them up to a month to digest a meal. Their extra-slow digestion means they might only take a dump once a week, if not once a month. The poor creatures are always incredibly constipated.

So when they do poop, the result is enormous. A single bowel movement could be up to a third of the sloth’s body weight—a measurement that’s 282 percent of what scientists would expect to see in an animal of that size, according to one sloth-poop analysis from 1995.

The particular bathroom routine depends on the type of sloth, though. Two-toed sloths are often fine with letting it rip from the forest canopy (woe to any animals that might be hanging out below), while three-toed sloths determinedly make their way to the ground to do their business. Once they get down to the forest floor, they dig a hole, take a poop, then cover it up with leaves and make their way back up to the canopy.

That’s where the danger comes in. Pooping on the ground is one of the most risky things a sloth can do in life. By one estimate, up to half of sloth deaths can be linked to these rare bathroom trips.

Sloths can barely walk, thanks to their long claws and limbs that are designed to hang from trees; they don’t support their weight on the ground very well. (They have significantly less muscle mass than other mammals.) Instead, they crawl, dragging themselves forward with their forelimbs. That makes them laughably easy targets for predators.

Scientists aren’t entirely sure why three-toed sloths take this huge risk to poop. One study has suggested it could be related to the symbiotic relationship the animals have with the critters that live in their hair, which include a specific type of potentially nutritious algae that may benefit from the journey to the ground.

That hypothesis is fairly controversial among sloth experts, though, because it’s not clear that the sloths actually eat this algae, or that it makes any kind of real impact on their diet.