The idea of throwing poop is gross for multiple reasons: you have to touch poop, it will touch someone else, and there will be inevitable mess. But for chimpanzees, it’s common behavior.
First off, the Jane Goodall Institute of Canada says it’s important to realize that the behavior is not common in free-roaming, wild chimps. They do throw things, but they typically stick to rocks or branches when looking for a way to express their annoyance, leaving their feces where they fall.
Whereas for chimps in captivity, there just often aren’t many options when they want to give something a good toss except poop, which is typically abundant.
Chimps throw things when they’re feeling frustrated or anxious, but they’re also smart enough to realize that they can elicit a reaction – horror and disgust, perhaps surprise – when they launch a turd at a zoo employee or a guest.
A 2012 study found that chimps who display good aim had a better-developed motor cortex, and better communications between that cortex and Broca’s area, a portion of the frontal cortex that helps process language in humans. Which is all to say, they were typically the better communicators in their peer groups.
A second study backs up the idea that smart chimps toss poo, by proving that the action is likely premeditated. The study was based on Satino, a chimp at Sweden’s Furuvik Zoo, who enjoyed frightening away visitors by tossing rocks at them. Researchers found that he stockpiled rocks every day before the zoo opened so that a) he would be well-armed and b) no zookeepers would be there to intervene.
Other chimps, though, have been seen pooping directly into their hands and then holding it as they wait for some human to annoy them.
Be careful when viewing the chimps, people. They might find you annoying and use whatever they’ve got at their disposal to make their opinion known – and if you end up wiping poop off your body in a zoo bathroom, I doubt the fact that the chimp who threw it is probably the smartest one of the bunch is going to be much of a comfort.