In Zambia, a group of chimpanzees is getting attention for a bizarre and hilarious habit. They’ve started decorating themselves with blades of grass. Not by weaving them into anything—just sticking them in their ears. And sometimes, their butts.

Researchers at the Chimfunshi Wildlife Orphanage have been watching this unfold for years. It started back in 2010 with a chimp named Julie, who began sticking long blades of grass into her ears. After her death in 2013, her son and a few others kept the trend going. The fashion statement seemed to mean nothing, functionally speaking, but it spread.

Then came Juma. In 2023, this male chimp took things to the next level by wedging grass into his rectum and letting it dangle like a tail. Within a week, his entire group joined in. According to a new study published July 4 in the journal Behaviour, it had nothing to do with hygiene or health. It was pure social signaling.

The Newest Chimpanzee Fashion Is a Blade of Grass in the Butt

“In captivity, they have more free time than in the wild,” said Edwin van Leeuwen, one of the researchers. “They don’t have to stay as alert or spend as much time searching for food.” Which means more time for, apparently, rear-end accessorizing.

The study suggests this kind of mimicry serves a more meaningful purpose. “By copying someone else’s behaviour, you show that you notice and maybe even like that individual,” van Leeuwen said. “So, it might help strengthen social bonds and create a sense of belonging within the group, just like it does in humans.”

This isn’t the first time chimps have been caught behaving in ways that feel eerily familiar. Earlier this year, a separate study documented wild chimps in Guinea-Bissau drinking fermented African breadfruit with about 0.61% alcohol content. The apes took turns sipping from the fruit, a possible sign of early bonding rituals centered around sharing food—and maybe even a buzz.

“For humans, we know that drinking alcohol leads to a release of dopamine and endorphins,” said ecologist Anna Bowland. “Feelings of happiness and relaxation follow.” The chimps may not have been tipsy, but they were certainly social.

It’s easy to forget how close they are to us. Then one sticks a leaf in their butt, and suddenly it all makes sense.