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.

Scientists studying camera trap footage from Jicarón Island spotted something unusual: a capuchin monkey carrying an infant howler monkey on his back. Now, they’re trying to learn what it means.