個水老鼠 A Water Rat Slips Through
變作個小螃蟹兒過去罷。也不好，恐師父怪我出家人腳多。」即變做一個水老鼠，颼的一聲攛過去，從那出水的溝中，鑽至裡面天井中。变作个小螃蟹儿过去罢。也不好，恐师父怪我出家人脚多。」即变做一个水老鼠，飕的一声撺过去，从那出水的沟中，钻至里面天井中。
逐句解 Line by line
Let me change into a little crab and go across, then.
The second candidate, and it lasts one line. A crab genuinely would be the right creature for a drain, which is what makes the objection funnier.
That is no good either — I am afraid the master would think ill of a man in holy orders having so many legs."
Thirteen characters to rule out a crab on the grounds of leg count. There is no precept about legs. Wukong has invented a scruple, and the novel lets him do it with a completely straight face.
So he changed into a water rat, went whisking across with a rush, and from the outfall drain bored his way through to an inner courtyard.
The choice he settles on has more legs than a snake and fewer than a crab, and no scruple attaches to it at all. 颼 is the sound of something going past fast. 天井, a heaven-well, names a small open courtyard with buildings closing it in on every side — so the cave has proper domestic architecture, courtyards and all.
The comedy of the three-way choice is that only the third is arrived at without reasoning. He rejects the snake on doctrine and the crab on legs, and then becomes a rat without a word of self-examination.
Underneath the joke the novel is showing us something it rarely says outright: Wukong misses his teacher. He is deferring to the opinions of a man he believes is dead, about a decision nobody will ever see.