緊箍為咒 The Tightening-Band Spell
我頂上戴的這個箍兒，是觀音菩薩賜與我師父的，師父哄我戴了，就如生根的一般，莫想拿得下來，叫做緊箍兒咒，又叫做緊箍兒經。他『舊話兒經』，即此是也。但若念動，我就頭疼，故有這個法兒難我。師父，你莫念，我決不負你，管情大家一齊出去。」我顶上戴的这个箍儿，是观音菩萨赐与我师父的，师父哄我戴了，就如生根的一般，莫想拿得下来，叫做紧箍儿咒，又叫做紧箍儿经。他『旧话儿经』，即此是也。但若念动，我就头疼，故有这个法儿难我。师父，你莫念，我决不负你，管情大家一齐出去。」
逐句解 Line by line
"This band I wear on the crown of my head was given to my master by the Bodhisattva Avalokiteśvara. My master tricked me into putting it on, and now it is as though it had grown roots—there is no thinking to take it off. It is called the Band-Tightening Spell, and also the Band-Tightening Sūtra.
The band was a trick from the start, and Wukong says so without bitterness. 觀音菩薩 is the bodhisattva Avalokiteśvara, Guānyīn, with 觀 as guān; she gave the fillet to Sanzang, who talked Wukong into putting it on. 就如生根的一般, "as though it had grown roots," is exactly the right image for something you cannot get off your own head. 箍兒 takes the diminutive suffix 兒, ér; 拿得下來, "able to get it off," takes the toneless 得, de, marking possibility.
"His 'Old-Talk Sutra'—this is precisely it.
即此是也, jí cǐ shì yě, "this is precisely it" — a bookish flourish, and slightly absurd in the mouth of a monkey identifying his own headache.
"But if he sets to reciting it, my head aches at once; so he has this method to plague me.
念動, niàn dòng, is to set about reciting. 難我, nán wǒ, is to make things hard for somebody, with 難 as the verb nán, "to press, to vex." 法兒 again takes 兒, ér.
"Master, do not recite it—I will surely not fail you; depend upon it, we shall all get out together."
And so a bargain: don't recite, and I'll get us all out. 我決不負你, "I will certainly not let you down." 管情, guǎn qíng, is "depend on it, rest assured" — the language of a man selling you something.
This is the chapter pausing to explain its own machinery. The golden fillet cannot be removed, and at a few words from Sanzang it closes on Wukong's skull; that is the arrangement by which a creature who once fought Heaven can be kept walking west with a nervous monk. Played here for laughs, it is elsewhere in the novel a genuinely uncomfortable device, and readers have argued about it for four hundred years.
What makes the scene work is that the threat is never carried out. Sanzang raises it, Wukong answers it with a promise, and the promise is kept: he does get them all out, that same night. For all the bickering, the leash stays slack, and the loyalty it was meant to compel turns out to be there anyway — a point the chapter will make far more strongly when Wukong offers his own back to the whip.