Getting sleep is just as important for animals as it is for us humans. But while we can feel quite safe in our beds, ducks need to stay alert even while they are sleeping so that they can flee in time if danger approaches. So nature has equipped them with a special ability. While a flock of ducks rests together, those sleeping at the edge of the group only fall into a half-sleep. They keep the eye facing outwards open while the eye facing their fellow ducks is closed. This way they get the sleep they need and at the same time protect the ducks in their group from being surprised by a predator.