00:00A whale has to keep coming back to the surface to breathe,
00:02so how can it sleep without drowning?
00:04The secret is called unihemispheric sleep.
00:06Instead of shutting down its entire brain,
00:08a whale rests one half while the other half stays active.
00:11The awake side keeps the whale swimming and controls its breathing.
00:14After some time, the two sides can switch roles.
00:16That means a whale can rest while still staying aware of its surroundings
00:19and surfacing for air.
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