事实上，骚痒和抓挠帮助动物去掉寄生虫、植物体或其它不想要的垃圾。
In nature, itching and scratching help animals get rid of parasites, plant material, or other unwanted baggage.
动物有寄生虫或携带各种各样的病毒。一旦传染给人类，这将会是非常麻烦的事。
Animals have parasites or carry a variety of viruses. Once transmitted to humans, it would be a very troublesome thing.
寄生虫的一个典例是绦虫，它生活在更大的动物的肠道内，从宿主那里吸收营养。
An example of a parasite is a tapeworm that lives inside the intestines of a larger animal and absorbs nutrients from its host.
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