Fei

Tai Mountain in the fourth eastern guideway — a namesake of, and distinct from, the Mount Tai where the tongtong lives — carries gold, jade, and privet on its slopes. Its beast is the fei: an ox's body under a white head, a single eye in the face, and a snake's tail behind. The text records no attack, only aftermath: 'where it wades, water dries up; where it walks, grass dies.' The streams it crosses fail, the turf it treads withers on the spot, and its appearance announces pestilence for all under heaven.

Most horrors in the classic either harm people or warn them; the fei folds the two together. Wherever it passes, the landscape rehearses the plague in advance — water gone, vegetation dead — and the sickness follows. Guo Pu's commentary ranks it among the calamity beasts, and in later compilations on omens of epidemic the fei stands near the head of the list. It also closes the fourth guideway's roster of disasters: the heyu governs flood, the bo fish drought, the fei pestilence — three catastrophes, each with its officer.

In pre-Qin texts the character 'fei' separately names a small insect counted as a blight; the Spring and Autumn Annals records 'in autumn, there were fei' as a portent worth writing down. Insect and beast share the name and nothing else, and commentators have long set the two entries side by side to keep them distinct. The white-headed, one-eyed ox of Tai Mountain is the larger and more thorough of the two disasters.