鋪兵之鑼 The Gong Of A Post Courier
急現本像下來，又看時，只聽得丁丁東東的一個銅鑼聲響。卻道：「我走錯了路也，這裡不是妖精住處。鑼聲似鋪兵之鑼，想是通國的大路，有鋪兵去下文書。且等老孫去問他一問。」急现本像下来，又看时，只听得丁丁东东的一个铜锣声响。却道：「我走错了路也，这里不是妖精住处。锣声似铺兵之锣，想是通国的大路，有铺兵去下文书。且等老孙去问他一问。」
逐句解 Line by line
He resumed his own form in haste and came down, and looking about him again he heard nothing but the ding-ding dong-dong of a brass gong sounding.
聽得 takes dé — the character has fused into the verb of perceiving and stopped doing any work of its own. 丁丁東東 is the gong written down as a noise. It arrives in a chapter that has just spent four lines of verse on things that cannot be seen, and the first information Wukong gets on this mountain comes through his ears.
He said: "I have taken the wrong road. This is no fiend's dwelling."
走錯了路 — taken the wrong road — is flatly untrue. He is on precisely the mountain he was sent to. The narrative hands him the mistake and does not correct it, and lets him reason forward from it for two more sentences.
"That gong sounds like a post courier's gong. I take it this is a high road running through to the capital, and there is a courier out delivering despatches."
鋪 is pù, a relay station on the official road network, not the pū of spreading something out — and 鋪兵 is the runner attached to one. The inference is sound at every step and wrong at the end, which is only possible because the reasoning is good: that gong belongs to the postal service, the postal service runs on highways, highways lead to capitals.
"Let Old Sun go and put him a question."
問他一問, verb either side of its measure again. He has put down fire, smoke and sand between them, and proposes to deal with a gong by asking it a question.
Wukong's misreading is built out of perfectly good reasoning. A gong of that kind belongs to the postal service; the postal service runs on high roads; high roads lead to capitals; therefore this is a road and not a lair. Every step follows, and the conclusion is false, because the premise he never examines is that a demon would not own a gong.
It is worth setting beside the king's mistake earlier. He saw a cup thrown and concluded he had given offence — reasoning correctly from what he could see and wrongly about what it meant. Wukong now hears a gong and does the same thing. This chapter has a habit of letting competent people be exactly as wrong as their evidence permits.