Humans are often thought to be insensitive smellers compared with animals, but this is largely because, unlike animals, we stand upright.
=Compared with animals, humans are often thought to be insensitive smellers , but this is largely because, unlike animals, we stand upright.
参考译文：和动物比起来,人类经常被认为嗅觉不敏感.但很大程度上是因为我们和动物不同,我们是直立行走的.
compared with animals, 为过去分词作状语，还可以提前到句首，不能使用动词原形，动词原形不能作状语，只能作谓语。
