就是洞門 Eight Rules Knows The Door
八戒道：「你原來不曉得。我前年請他去時，先在洞門外相見。後被我說泛了他，他就跳下，去洞裡換衣來時，我看見他將身往水裡一鑽。那一股瀑布水流，就是洞門。想必那怪將我們包袱收在那裡面也。」八戒道：「你原来不晓得。我前年请他去时，先在洞门外相见。后被我说泛了他，他就跳下，去洞里换衣来时，我看见他将身往水里一钻。那一股瀑布水流，就是洞门。想必那怪将我们包袱收在那里面也。」
逐句解 Line by line
Eight Rules said: "So you did not know, after all.
Nine characters, and the tone is unmistakable: Eight Rules has finally got hold of something nobody else knows.
The year before last, when I went to invite him back, I met him first outside the cave door.
相見 takes xiāng, met each other, where the automatic reading gives xiàng. He is remembering chapter thirty-one, when he came to this cave to fetch Wukong back from exile.
Afterwards, when I had talked him round and he jumped down and went into the cave to change his clothes, I saw him take his body and dive straight into the water.
說泛了他, talked him round — literally floated him along, which is a nicely oily way of describing a persuasion. 將身 uses 將 to introduce what is being handled, and takes jiāng.
That single cataract of flowing water is the cave door.
Eleven characters, and they answer the question that defeated Sha Monk two thousand characters earlier.
It must be that the monster has put our bundles away in there."
Both 那怪 and 那裡面 are pointing at something, so both take nà — against the questioning nǎ of 看那個 back at the fillet test.
Eight Rules supplies, casually and from memory, the one piece of information the chapter has been withholding since the second passage. The waterfall is the door. He knows because he once came to this cave to coax Wukong out of retirement and watched him dive straight through it — a domestic detail from an old errand, dug out now as the answer to a practical problem.
The pattern holds: in this chapter the useful knowledge keeps arriving from unglamorous sources. The Bodhisattva could not tell the pair apart. The Jade Emperor's mirror could not. But Eight Rules knows where the front door is, because he has been here before. Ordinary acquaintance keeps outperforming supernatural discernment, and the novel has not yet said so out loud.
你原來不曉得 also carries a small flick of superiority, which is entirely in character. Eight Rules has spent the chapter turning up late and being of no use, and this is his one moment of knowing something the others do not. He makes the most of it.