The good Pilgrim, with a faint droning buzz, flew to the top of the Tang Monk's head, and there saw a bedbug the size of a bean feasting on his master; hurriedly he pinched it off with his hand and scratched and rubbed the spot for him.

嚶的一聲 is the thin whirring hum of a small insect, one of the sound-words the storyteller keeps for Wukong's gnat form. He finds a bedbug 豆粒大小, the size of a bean, feasting on his master. 撓撓摸摸 — scratch-scratch, rub-rub — doubles both verbs to catch the fussing motion of a nurse.

The elder, neither aching nor itching, sat bolt upright above.

端坐 is to sit foursquare and upright, the posture of a man in perfect control, which he now is, because the bug is gone. 那長老: 那 = nà, 長 = zhǎng.

The Pilgrim thought to himself: "A monk's pate is bald — not a louse could find a foothold on it, let alone this bedbug.

Wukong reasons it out, and the reasoning is good detective work: 和尚頭光, a monk's head is shaved and gleaming, so 虱子也安不得一個 — not even one louse could get a footing. 安不得 joins verb to result with 得 = de. 虱子 takes the light 子 = zi.

It must be that Daoist working some sleight to harm my master.

弄的玄虛 is a lovely phrase for it — working a bit of hocus-pocus, conjuring smoke and mystery. 那道士: 那 = nà.

Aha — it's a stalemate anyhow, with no telling win from loss; let old Sun go and give him a taste of it!"

枉自也不見輸贏 — for all this sitting, no winner is showing. So: 弄他一弄, give him a taste of it. Splitting the verb around its own object like this is the Chinese way of marking something light and deft, the flick of a wrist rather than a blow.

This Pilgrim flew up, alighted upon the beast-head atop the golden hall, gave his body a shake and a change, turned into a centipede seven cùn long, and went straight to sting the Daoist once in the hollow of his nose.

One sting for another, exactly measured. A bedbug on the master's scalp is answered by a centipede in the Immortal's nostril. 落下 is luò, "to alight," not the colloquial là of leaving something behind. 七寸長: here 長 is cháng, length, not the zhǎng of growing — and 寸 stays as cùn, the Chinese inch of roughly three centimetres, so the creature is a good hand's-length of centipede. 飛將上去: 將 = jiāng, pointing the flight upward.

The Daoist could not keep his seat: with a somersault he pitched down headlong and all but lost his life, saved only by the crowd of officials, high and low, who caught him up.

觔斗 is a somersault — 觔 is an old way of writing 筋, sinew, and its 斗 is dǒu. 翻將下去 again uses 將 = jiāng for direction. 喪了性命, nearly lost his life, with 了 the light le marking it done. Note who catches him: the officials, in a crowd. The court is still on his side.

The king, greatly alarmed, at once ordered the Grand Preceptor then on carriage-duty to lead him off to the Hall of Literary Glory to wash and dress.

著 is zhuó here — the same sound met in 著實 at the chapter's opening, now doing its other job: to order somebody, to dispatch them. 當駕 is dāng jià, on carriage-duty, the officer of the day attending the imperial coach. 梳洗 is to comb and wash. A National Preceptor has just fallen off a tower and nearly died, and the king's response is to send him for a tidy-up.

The Pilgrim, riding his auspicious cloud still, bore his master down before the steps — and so the elder had already won.

The narrator certifies the result on the contest's own terms: 已是長老得勝, the elder had already won — 長 = zhǎng, 得 = dé, "gained the victory." Won by a trick, and the ledger still reads clean, because the other side cheated first. 將師父馱下: 將 = jiāng.