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NOVA: Mysteries of Sleep Like virtually every other animal, humans need sleep to survive. But why? What do we gain from spending nearly a third of our lives in such a defenseless state? And what's at stake if we sleep poorly? The functions of sleep have long been something of a mystery. But now scientists are peering deep into the brain to see what happens while we snooze. One ...。Prepare to be awed by the once-in-a-lifetime meeting experienced by a group of divers and photographers in Hawaii, who hung out near a sperm whale carcass to photograph the tiger sharks who came to feed. Suddenly, everything went quiet, and the tiger sharks vanished. A gigantic shadow appeared in the distance. On the program, Dr. Chris Lowe, director of the Shark Lab at Califor...。