小的口訣 He Lacks the Shrinking Formula
拿在手中，仔細看了又看，比前番假的果是不同。只見祥光晃晃，瑞氣紛紛，上有三十六縷紅絲，穿經度絡，表裡相聯。原來行者只討了個長的方法，不曾討他個小的口訣，左右只是那等長短。沒奈何，只得搴在肩上，找舊路而回，不題。拿在手中，仔细看了又看，比前番假的果是不同。只见祥光晃晃，瑞气纷纷，上有三十六缕红丝，穿经度络，表里相联。原来行者只讨了个长的方法，不曾讨他个小的口诀，左右只是那等长短。没奈何，只得搴在肩上，找旧路而回，不题。
逐句解 Line by line
He took it in his hand and looked at it carefully over and over: set against the counterfeit of the time before it was plainly not the same.
仔 is zǐ in 仔細, careful, not zǎi. 看了又看 doubles the verb across the perfective — looked and looked again.
He saw only an auspicious light dazzling and a lucky vapour thick about it, and on it six-and-thirty strands of red silk, threaded through warp and net, inner and outer answering each other.
晃 is huǎng at both characters — of light that dazzles, not of a thing that sways. 度 is dù and 相 the each-other xiāng. The thirty-six strands, set against the seventh she named, give the fan a mechanism rather than a mere power.
It turned out that the Pilgrim had asked only for the method of making it long, and had not asked her for the formula of making it small; so it stayed at that length, do what he would.
Both instances of 長 here are cháng, first adjective then noun — 長的方法 standing in parallel with 小的口訣 — where the same character was the verb zhǎng in the previous passage. 原來 marks the discovery as belated, which it spectacularly is.
Having no help for it, he could only hoist it onto his shoulder, find the old road and go back; of which no more.
沒 is méi and 只得 takes dé. 不題 — no more of this — is the storyteller's formula for putting a thread down, the answering move to the 卻說 that picks one up. It closes the Great Sage's part in the chapter, and he goes out of it carrying something he cannot put away either.
This is the real ending of the chapter for the Great Sage, and it is a defeat dressed up as a success. He has the true fan, he has the working charm, and he has asked one question too few. The Rākṣasī told him how to make it large because that is what he asked; nobody told him how to make it small again, and the novel notes the omission in a single sentence beginning 原來.
The failure is of a piece with everything else he has done across these two chapters. He concealed his errand from the Jade-Faced Princess and started a brawl; he named the Iron-Fan Princess to the Bull King and lost a pardon; he got the fan out of the Rākṣasī and did not think to ask for the second half of the procedure. Every time, the intelligence is adequate and the interrogation stops one question early.
The image the chapter leaves him with is domestic and faintly absurd: the Great Sage Equal to Heaven walking home along the old road with a fan the height of a house on his shoulder, unable to fold it. 沒奈何 — having no help for it — is the same phrase used of him at the drinking table, and it is the last thing said about him before the narrative leaves to follow the Bull King.