你能从一大群游客中轻而易举地把美国人认出来，只要看看他们脸上那出于本能的咧嘴笑就知道了。
You can pick out the Americans in a crowd of tourists by their reflexive grins.
当一群人笑的时候，人们会本能地去看那群人中让他们觉得最亲近的人。
When a group of people laugh, people will instinctively look at the person they feel closest to in that group.
但当我们漫游在一些随处可见的最险的区域中时，我们看到了驱使着它的动物群中的生命的同样的力量和本能。
But we see the same forces and instincts driving the lives of its fauna as we tour some of the most forbidding territory anywhere.
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