行不更名 I Do Not Change My Name
這沙僧見了，大怒道：「我老沙行不更名，坐不改姓，那裡又有一個沙和尚？不要無禮，吃我一杖！」好沙僧，雙手舉降妖杖，把一個假沙僧劈頭一下打死，原來這是一個猴精。这沙僧见了，大怒道：「我老沙行不更名，坐不改姓，那里又有一个沙和尚？不要无礼，吃我一杖！」好沙僧，双手举降妖杖，把一个假沙僧劈头一下打死，原来这是一个猴精。
逐句解 Line by line
This Sha Monk saw it and flew into a rage: “I, old Sha, do not change my name when I walk nor alter my surname when I sit. Where is there another Sha Monk?
He reaches for the standard boast and it lands very strangely. 行不更名, 坐不改姓 -- I do not change my name when I walk nor my surname when I sit -- is the stock declaration of an honest man with nothing to hide, the thing a fighter says when he announces himself. 更 takes gēng, to alter, not the comparative gèng, and 行 stays xíng. 那裡又有 is the rhetorical 那, nǎ. He is asserting that his identity cannot be falsified, to a thing that is wearing it.
“Do not be insolent — take a stroke of my staff!”
Eight characters, and the argument is over.
Fine Sha Monk! He raised the demon-quelling staff in both hands and brought it down full on the head of that false Sha Monk and killed him — and it turned out he was a monkey-spirit.
降妖杖 takes 降 at xiáng, to subdue -- an automatic reading gives jiàng, to descend, and the guard list forces the decision. 劈頭 is full in the face, and 一下 takes the ordinary tone change to yí. One blow, and the copy is a dead monkey-spirit.
Sha Monk's boast is the one the novel's fighters make when they announce themselves -- I do not change my name walking nor my surname sitting -- and it has never been aimed at anything like this. He is asserting the fixity of his own identity to a thing that is wearing it. The line is a commonplace everywhere else in the book and lands very oddly here.
The killing is instant and gives him no trouble at all, which is itself information. One blow, and the copy is a dead monkey-spirit. Whatever the false king has assembled, it is not made of anything that can withstand the originals -- a fact that will matter more in the next chapter than it does in this one.