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... n August 2023, at the Chimfunshi Wildlife Orphanage Trust sanctuary in Zambia, a trendsetting chimp named Juma was seen sticking a piece of grass into his ear, deep enough to stay there on its own. Within a week the fad went viral, as four other chimps in the group started copying his unusual accessory.

Not to be outdone, later that month Juma debuted a risqu variation: he inserted a blade of grass into his rectum, and left it dangling. This unorthodox trend also caught on, with five other chimps adopting the strange new fashion.

The behavior fascinated researchers observing the captive chimpanzees (Pan troglodytes) . The grass didn't seem to serve a biological purpose -- they weren't scratching itchy ears or butts, for example. Instead, the team hypothesizes that it might serve a social purpose.

"By copying someone else's behavior, you show that you notice and maybe even like that individual. So, it might help strengthen social bonds and create a sense of belonging within the group, just like it does in humans," says Edwin van Leeuwen, biologist at Utrecht University in the Netherlands. ...