Chimpanzees in Zambia have been engaging in the seemingly pointless behavior of sticking grass into their ears. This behavior was exhibited by two distinct groups of chimps, who had no crossover. So, how did it come about?

“Both groups where chimps put blades of grass in their ears, had the same caretakers. These caretakers reported that they sometimes put a blade of grass or a matchstick in their own ears to clean them,” Van Leeuwen says. “Caretakers in the other groups said they did not do this. The chimps in the one group then figured out to stick the blade of grass in another place as well.”

What exactly was that other place?

But in the new group, the grass-in-orifice trend did not stop there. While five of the eight chimpanzees in the new group stuck grass in their ears, six of the eight also let a blade of grass dangle from their behinds. The researchers found no evidence that the chimpanzees were bothered by their ear or behinds and used the blades of grass, for example, for relieving an itch.

Perhaps more questions should be asked of that group of caretakers.