《水经注·卷三十七》
常有爬山越岭的人，手攀树木，侧足而行，但不知是什么人。
每有陟山岭者，扳木侧足而行，莫知其谁。
There are often people who climb mountains and cross ridges, climbing trees with their hands and walking sideways, but it is not known who they are.