Capuchins are also known for developing odd social rituals across their range. Scientists studying mainland populations have noted monkeys poking fingers up each other’s noses and in each other’s eyes, biting tufts of fur off of each other, drumming on a partner’s belly or back, and sticking hands in other capuchins’ mouths, says Perry.

A group of white-faced capuchins on a remote island have started stealing infants from another primate species, and researchers don’t know why