When it comes to taking a nap, dolphins have several alternatives. They are often seen in pairs to take turns sleeping, so that one dolphin sleeps with the other dolphin being carried away by the wake, which keeps it moving and alert to any danger .
But undoubtedly the most surprising thing about these marine mammals is their ability to put half the brain asleep and stay awake with the opposite hemisphere, which is responsible for exerting control over vital functions, especially breathing. During these "unihemispheric" sleep periods, dolphins slow down their metabolism and become practically immobile. The half of the brain that remains active during sleep can keep the dolphin on course and prevent it from adrift.
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