A group of English mandrill monkeys has started doing facepalms. The monkeys live in a zoo in Colchester, England, and eight of them frequently raise one or both of their hands to cover their eyes. They might be the only ones in the world who perform this distinctive gesture.

Liz Butcher, a former keeper at the zoo, was the first to notice the gesture in a female mandrill called Milly, way back in 1999. Milly still does it and it’s caught on among seven other individuals within the group (out of 23), without any training or encouragement from the other keepers.

But why are they doing it? It’s unlikely that they’ve found something stupid on the Internet. Nor are the