Multiple choice general knowledge How do ducks sleep floating on their backs to balance their weight balancing on one leg with one eye open on the back with both eyes closed Reveal answer Fill a bubble to check yourself C Correct answer Explanation Ducks practice unihemispheric slow-wave sleep, meaning they sleep with one brain hemisphere awake and one eye open to stay alert for predators. They can switch hemispheres, allowing half their brain to rest while remaining vigilant.