Have you ever wondered how dolphins sleep? Probably not; but think about it. They are mammals that live in the water and breathe oxygen. They have to surface every once in a while to breathe and at its longest may only stay underwater for around fifteen minutes.
So, how do they sleep?
With one eye open and one eye closed. Not literally. Rather they shut down one hemisphere of their brain at a time. In a 24-hour period each side gets about 4 hours of “unihemispheric slow wave sleep.”
One side of the brain will rest and recover while the other keeps the dolphin functioning and breathing per usual. Cool stuff.