Some monkeys in a British zoo have been getting up to some very unusual behavior. They cover their eyes with their hands when the Sun isn't even shining down on them, and they keep their eyes open the whole time, suggesting this isn't a physical reaction but actually a form of social interaction. The zookeepers suspect the monkeys are actually telling their peers to leave them alone, essentially making a "Don't Disturb" sign with their hands. Even more intriguingly, these particular mandrill monkeys are the only members of their species that display this behavior, suggesting the gesture is purely social in nature, something that's very rare outside humans. Check out the full story at LiveScience.