Ershu

Danxun Mountain, in the first guideway of the Northern Mountains, grows ailanthus and cypress, wild chives and rocambole, and yields cinnabar pigment. Its beast is at base a rat, but it wears a hare's head, its body has the build of an elaphure deer, and its voice is the howl of a dog. Strangest is its manner of flight: 'it flies by means of its tail' — no wings, just the one appendage. The classic appends the pharmacology: eating its flesh prevents distension of the belly and guards against the hundred poisons.

Flying beasts in the classic each have their own technique. The feishu of Tianchi Mountain 'flies by means of its back'; the ershu flies by its tail. Later commentators and naturalists reached for the flying squirrel — the membrane-winged glider that steers with a plume of a tail — and the match with 'flies by its tail' is fair, though the hare's head and deer's body refuse to cooperate. An identification is only ever an identification.

The phrase 'guards against the hundred poisons' places the ershu high in the classic's pharmacopoeia. Most animal remedies in the book treat a single complaint — abscesses, warts, sore throats, one ailment apiece. A universal antidote is rare. A small beast combining rat, hare, deer, and dog, which flies on its tail and neutralizes every poison: for one entry, Danxun Mountain packs an uncommon density of marvels.