The aside is a fossil of live performance. A storyteller who has just made a horse bolt at Wukong's shout can hear the obvious objection coming — Bajie was shouting too — and stops to dispose of it before going on. The 世德堂本 prints it as a paragraph of its own, and it reads as one: a complete question and answer that could be lifted out without disturbing the story on either side.

What the answer supplies is not really an explanation. The 弼馬溫 appointment back in chapter four was the insult that started Wukong's rebellion, the title he could not stand to hear; here it is quietly repurposed as a piece of practical stable lore. The novel has been calling him 弼馬溫 in mockery for most of the journey, and this is the one place where the job turns out to have been good for something.

There is a real folk belief underneath it. Keeping a monkey with the horses to keep them healthy is attested well before the novel was written, and the pun that gave Wukong his title — 弼馬溫 for 避馬瘟 — is that belief squeezed into three characters. The aside works in both directions: it explains the horse by the myth, and the myth by the horse.