Some say that when the yelping kind [of fox] are old, they become monsters. they wear a dry skull on their heads, clothe themselves with oak leaves, and assume a human guise. These creatures do harm in countless ways. People set fire to the mountains and dig up their burrows, grasping arrows and driving their hounds, thinking if fox kind is eradicated, monstrosity will cease.
They do not know that although foxes can become monsters, they do not necessarily do so. Once in a while one becomes a monster, but they do not all become monsters. …
Some say that those who get old and become monsters are called pi foxes or “spirit” foxes. They look like cats and are black. There are a lot of them in the north. They are probably another variety.
He Bang’e, 1791, in Occasional Records of Conversations at Night