Shocking! Dolphins sleep with one eye open
Dolphins are believed to be among the brightest creatures on the world, probably due to their ability to save mental energy. Because they must always be on the alert for predators, marine animals have devised a clever mechanism that allows them to maintain partial consciousness while a portion of their brain sleeps. Researchers investigated if this "half sleep" affects the animals' awareness during the day, but discovered that they were as attentive and observant as before after five days of having their nocturnal alertness regularly evaluated.