瞌睡蟲 The Sleep Bug Goes In
變作一個瞌睡蟲，輕輕的放在他臉上。原來瞌睡蟲到了人臉上，往鼻孔裡爬，爬進孔中，即瞌睡了。变作一个瞌睡虫，轻轻的放在他脸上。原来瞌睡虫到了人脸上，往鼻孔里爬，爬进孔中，即瞌睡了。
逐句解 Line by line
It turned into a sleep bug, and he set it gently on her face.
A 瞌睡蟲 is exactly what it sounds like — a bug that makes you sleep, and one of the standard items in Wukong's kit. Think of it as slipping something into a drink, except that the something walks. 的 is the neutral de.
Now once a sleep bug reaches a person's face it crawls towards the nostrils,
The narrator stops the action to explain the mechanism, which is the chapter-book equivalent of a cutaway. 原來 is the word that opens these asides — as it happens, the fact is.
and once inside the hole, sleep comes at once.
Eight characters to finish the explanation. 中 is zhōng, inside; 了 is the neutral le, marking that the sleeping has arrived.
Thirty-eight characters, and the middle third of them is a footnote. The narrator puts the story on hold to explain how a sleep bug works — it goes for the face, it heads for a nostril, it gets in, you sleep — and delivers the whole mechanism in the flat tone of someone explaining a household appliance.
That flatness is the joke. This is a knockout drug administered by an insect climbing up a fox spirit's nose, and the prose treats it as a matter of common knowledge, needing only a brief reminder for anyone who had forgotten. 瞌睡蟲 appears three times in this chapter, and here, where it is introduced, nothing marks it out as strange.
It is also worth noting what the sleep bug is not. Wukong has a five-hundred-year reputation and an iron rod, and the tool he reaches for here is soporific, reversible and small enough to sit on a cheek. He is not here to fight anyone yet.