《论衡·卷二十二·纪妖篇》
凡是妖象出现，有的是像人形的鬼，有的是人像鬼而活动，其实质都是一样的。
凡妖之发，或象人为鬼，或为人象鬼而使，其实一也。
Whenever an ominous sign appears, sometimes it is like a ghost in the shape of a human, and sometimes it is a human who acts like a ghost, but in essence they are all the same. 