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Listen to part of a lecture from a Biology class.
请听生物课上的部分内容。
When we humans walk from place to place, we move on the Earth's surface, across the Earth's surface.
当我们人类从一个地方走到另一个地方时，我们是在地球的表面移动，或者横穿地球表面。
Many animals of course do the same thing.
当然很多动物也是这样。
Horses and dogs and cows and so on, all move on the surface, across the surface of the Earth.
马、狗、牛和其他动物都是在地球表面移动，横穿地球表面。
There are also, there are quite a few animals that have the ability to move from place to place underground, beneath the Earth's surface.
但也有一些动物可以通过地下从一个地方到达另一个地方，它们在地表以下移动。
This moving around underground is known as subsurface locomotion.
这种在地下四处移动的行为被称作地下运动。
Subsurface locomotion has a number of benefits.
地下运动有诸多好处。
One benefit of subsurface locomotion is that it enables animals to minimize their exposure to extreme temperatures.
其中一个好处就是：可以减少动物暴露在极端气温下的几率。
This is very helpful for animals that live in areas with harsh climates,
这对生活在严峻环境中的动物来说很有益处，
where it could be very dangerous to spend large amounts of time on the surface.
在这种严峻环境里，长时间待在地球表面是很危险的。
For example, in the Sahara Desert, in Africa,
比如，在非洲的撒哈拉沙漠里，
there's a type of lizard that's able to move beneath the surface, through the sand, very quickly.
有一种蜥蜴能够穿过沙子在地表以下移动，动作十分迅速。
Because this lizard can move so easily and so quickly underground,
由于这种蜥蜴在地下移动十分简单迅速，
it doesn't have to travel on the surface, where it would be exposed to dangerously high temperatures.
它并不需要在地面活动，否则将暴露在致命高温下。
Another benefit of subsurface locomotion is that it can help animals capture prey.
地下运动的另一个好处就是能够帮助动物捕食。
That's because animals on the surface can't see predators that are approaching underground.
这是因为地面上的动物看不见从地下接近它们的捕食者。
Our lizard in the Sahara Desert is again, a good example.
撒哈拉沙漠的蜥蜴同样又是很好的例子。
The way it works is, when an insect is walking nearby on the surface, it produces very subtle vibrations in the sand.
具体原理是这样的：昆虫在附近的地面移动时会在沙子中产生非常轻微的震动。
When the lizard senses these vibrations, it moves very quickly.
一旦蜥蜴感知到了这些震动，便会迅速行动起来。
Underground, where it can't be seen, toward the source of the vibrations.
它在地下朝着震源移动，而它的猎物却浑然不觉。
It then suddenly pops up directly under the insect and catches it completely by surprise.
接着它会猛得从昆虫下方直接冲出，完全出其不意地将猎物捕获。
