磨一磨 He Is Grinding It For You
他就著那澗崖石上，抄一把水，磨一磨，口裡又念一聲，說他那杠子到此還不曾顯個神通，他要磨明，就來打大王。我因此知他是孫行者，特來報知。」他就着那涧崖石上，抄一把水，磨一磨，口里又念一声，说他那杠子到此还不曾显个神通，他要磨明，就来打大王。我因此知他是孙行者，特来报知。」
逐句解 Line by line
He set to right there on the rock by the ravine wall, scooped up a handful of water, gave it a grind, and muttered aloud that his pole had not yet shown its power in all this time — he meant to grind it bright and then come and beat the Great Kings to death.
就著 takes the light zhe, the sense of making use of a thing right where it stands; the previous chapter wrote this same moment with plain 在. 還 is hái, still, the adverb — worth flagging because the chapter's own title uses the other reading of the same character. 磨一磨, grind-a-grind, is the casual doubling Chinese uses to make an action sound brief and offhand, which is precisely the wrong tone for what is being described.
That is how I knew he was Sun Wukong, and I came straight back to report it."
He closes the way a good subordinate closes: here is my inference, here is my diligence. 特來 — came specially — is the small flourish of someone who wants his errand noticed.
The lie is well built. Nowhere does Wukong claim the giant said he was Sun Wukong; he offers it as his own deduction, which is far harder to argue with and flatters the listeners by inviting them to agree. Then he hands them the threat in the giant's own reported words, so the menace arrives as testimony rather than as opinion.
Notice what he has cut. Told to the outer guard last chapter, the same lie ran to a hundred thousand demons killed, ten thousand more at the gate, and the three chiefs slaughtered to consecrate the weapon. Here it is four characters: 就來打大王, he is coming for the Great King. Wukong has not raised the threat, he has stripped it down to the only part this audience cares about, which is a better instinct than raising it would have been. And the chapter is about to show us how badly a careful liar can still come unstuck.