Seals have one of the coolest and most flexible sleep styles in the animal world. Because they split their lives between land and water, they’ve evolved different ways to rest depending on where they are. On land, they usually sleep like most mammals, lying on beaches or ice, completely relaxed, often in groups where they can stay warm and alert to danger. In the water, though, things get far more interesting. Many seals use a technique called unihemispheric slow-wave sleep, where only one half

How to pronounce HEMISPHERE in English | Collins