Not all sounds made by animals serve as language and we have only to turn to that extraordinary discovery of echolocation in bats to see a case in which the voice plays a strictly utilitarian role.

• 并非动物发出的所有声音都充当语言，我们只需要借助于蝙蝠回声定位的伟大发现，就可以发现声音起一个完全实际作用的情况。