不良之心 A Wicked Thought
行者暗喜道：「師父過得去了。」你道他怎麼就知過得去？他要起個不良之心，等那些人睡著，要偷他的衣服、頭巾，裝做俗人進城。行者暗喜道：「师父过得去了。」你道他怎么就知过得去？他要起个不良之心，等那些人睡着，要偷他的衣服、头巾，装做俗人进城。
逐句解 Line by line
Pilgrim was secretly delighted. "The master can get through."
過得去 puts 得 between a verb and its outcome, and read that way it takes de — the pattern that says an action is possible, can get through as against cannot. It is one of the commonest shapes in spoken Chinese and it hangs entirely on this one light syllable.
And how, do you suppose, did he know they could get through?
你道 is the storyteller turning to the room. The teller has been invisible for two pages and steps forward here purely to make you wait for the answer.
He was setting his mind on a piece of villainy: wait until those men were asleep, steal their clothes and headcloths, and go into the city dressed as laymen.
不良之心 is a mind not-good, and the phrasing is deliberately formal — the register of a moral judgement, applied to Wukong by the narrator with a perfectly straight face. 著 is zháo here, the reading for an outcome reached rather than a state held: 睡著 is to fall asleep, not to be lying asleep.
The pause before the answer is the oldest trick the storyteller has, and the novel uses it here for a punchline rather than a cliffhanger. How did he know? Because he had decided to commit a robbery.
The narrator calls it villainy and does not soften it. Wukong is about to rob sleeping travellers of their clothes so that his master can survive a city that would otherwise execute him, and the book lets both halves of that stand without resolving them. It is one of the reasons he is a better character than a straightforwardly heroic monkey would be.