In Costa Rica, there’s a group of white-faced capuchin monkeys that occasionally pull out each other’s hair, put their fingers in each other’s noses, and pry open others’ jaws. The behaviors have no obvious purpose, and at times, seem rather unpleasant and risky. One especially mischievous capuchin named Napoleon has been seen plucking cotton-ball sized tufts of hair from other capuchins on multiple occasions—which he then puts in his mouth.

“The other monkey would want to have their hair back, and so they would have to try to pry open his mouth,” says Susan Perry, director of the University of California Los Angeles’ Lomas Barbudal Monkey Project, a 30-year-long study of white-faced capuchins in Costa Rica’s Lomas de Barbudal