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There's an old saying that if you think you're in danger, you might ought to sleep with one eye open.
老话讲的好，如果你发觉自己处于危险之中，你会只睁着一只眼睡觉。
Well it turns out that many kinds of birds do just that.
事实上许多鸟类确实如此。
A group of scientists at Indiana State University studied mallard ducks to learn more about this trait.
印第安纳州立大学的科学家们通过研究野鸭对它们的这一习性有了更深入的了解。
They filmed a row of ducks while they were sleeping.
他们在鸭子们睡觉时进行拍摄。
Sure enough they found that a good part of the time the ducks at the ends of the row kept the eye facing away from the group open,while the eye toward the other ducks closed in sleep.
果不其然，他们发现队伍两端的鸭子朝外的那只眼睛长时间睁着，而朝向其它鸭子的那只眼睛闭着睡觉。
The ducks within the row were more likely to close both of their eyes to sleep.
而队列中间的鸭子们睡觉时则双眼紧闭。
The ducks at the ends of the line were actually controlling which side of the brain stayed awake,and which dozed.
队列两端的鸭子实际上在控制哪边的大脑保持清醒与休息。
They were engaging in what scientists call single-hemisphere sleep.
这是处于科学家们所称的单边睡眠状态。
The eye controlled by the sleeping side of the brain closed, while the active side kept its eye open and onthe lookout.
被睡眠状态大脑控制的眼睛闭上，而被运转状态大脑控制的眼睛睁开进行警戒。
You can see how this is good for the group and for the lookout duck as well.
这种习性对整个群体及放哨鸭子而言非常有帮助。
The group gets the protection from having someone pulling guard duty, while the guard duck is at least able to getsome rest.
鸭群通过一些鸭子放哨获得保护，而同时放哨的鸭子得到了一些休息。
