鏡腿無傷 Legs Bright as Mirrors
既這等，還打他罷。」小仙又打了三十。行者低頭看看，兩隻腿似明鏡一般，通打亮了，更不知些疼癢。此時天色將晚，大仙道：「且把鞭子浸在水裡，待明朝再拷打他。」小仙且收鞭去浸，各各歸房。晚齋已畢，盡皆安寢不題。既这等，还打他罢。」小仙又打了三十。行者低头看看，两只腿似明镜一般，通打亮了，更不知些疼痒。此时天色将晚，大仙道：「且把鞭子浸在水里，待明朝再拷打他。」小仙且收鞭去浸，各各归房。晚斋已毕，尽皆安寝不题。
逐句解 Line by line
"In that case, beat him again."
既這等, "in that case, then" — permission given as casually as it was asked for. 還 is hái, "again, still."
The little immortal laid on another thirty.
Another thirty. Sixty in all, and the narrator does not comment.
The Pilgrim bent his head and looked: his two legs were like bright mirrors, beaten to a shine all over, and he felt not the least ache or itch.
The punchline, and it is a visual one: sixty strokes of a soaked dragon-hide whip have polished his legs. 似明鏡一般, "like bright mirrors," 通打亮了, beaten to a shine all over. 更不知些疼癢, gèng bù zhī xiē téng yǎng, "did not feel the least ache or itch" — and 疼癢, pain-and-itch, is the smallest unit of sensation Chinese offers, so this is as thorough a denial as the language can make.
By this time the sky was growing dark, and the Great Immortal said, "Steep the whip in water, and tomorrow morning we shall flog him again."
The whip goes back in the water for the morning, which is the most chilling housekeeping in the chapter: the punishment is not finished, merely adjourned. 明朝 takes 朝 as zhāo, "morning." 鞭子 takes the toneless suffix 子, zi.
The little immortal put the whip away to steep, and each went off to his room.
各各歸房, each to his own room.
The evening meal over, all lay down to sleep—of that no more.
不題, no more of this — the storyteller putting the abbey to bed so he can turn to the four still tied to the pillars.
Sixty lashes of a soaked dragon-hide whip, and Wukong looks down to find his legs polished like mirrors. It is one of the novel's best comic images because it is entirely physical: not "he felt nothing" but "they had been buffed to a shine." The instrument of an immortal's justice has been reduced to a cleaning implement.
Nobody in the abbey notices. The Great Immortal, satisfied that a day's work has been done, has the whip put back to soak and adjourns until morning. That decision — punishment postponed rather than finished — is what gives the pilgrims their second night, and it is the only mistake he makes in the entire chapter.