撲搭不響 A Real Head Makes No Sound
行者道：「這是個假人頭。」八戒道：「怎認得是假？」行者道：「真人頭拋出來，撲搭不響；假人頭拋得像梆子聲。你不信，等我拋了你聽。」行者道：「这是个假人头。」八戒道：「怎认得是假？」行者道：「真人头抛出来，扑搭不响；假人头抛得像梆子声。你不信，等我抛了你听。」
逐句解 Line by line
Pilgrim said, "This is a false human head."
Nine characters, flatly stated, with no evidence offered yet. Wukong has worked it out and is about to prove it with a piece of practical physics.
Bajie said, "How can you tell it is false?"
In 認得, to recognise, 得 is dé — the reading it takes after a verb of perceiving, as against the little hinge it becomes after a verb of doing. This chapter has that recognising compound five times and every one is the same.
Pilgrim said, "Throw out a real human head and it lands with a soft flop and no ring to it.
撲搭 is a sound word — the dull, wet slap of something soft hitting stone. The novel is about to make an argument entirely out of acoustics, and it starts by giving the reader the noise a real head does not make.
Throw a false human head and it comes down sounding like a watchman's clapper.
梆子 is the hollow wooden block a night watchman beat to mark the hours, and every reader of this book would have known its sound from the street outside. In 拋得, 得 is de, hanging the resulting noise off the throwing. A semicolon joins this line to the last in the source, but the two are not a matched pair — the first has two clauses to the second one.
If you do not believe me, let me throw it and you listen."
The demonstration is offered as a courtesy. Wukong is not arguing his brother into agreement; he is proposing an experiment and inviting him to judge the result, which is a rather modern way to win a disagreement.
This is one of the most purely satisfying pieces of reasoning in the novel, and it requires no magic at all. Wood is hollow and rings; flesh and bone are dense and do not. Wukong has never seen this trick before and he works it out from first principles in the time it takes to pick the thing up.
The watchman comparison would have landed instantly on a Ming audience. The wooden clapper was the sound of the night hours being called, heard by everybody, every night. Saying a head sounds like one is not a poetic flourish — it is the most precise available reference for that particular knock.
Notice also what Wukong is doing socially. He could simply assert it, and he outranks Bajie by an enormous margin. Instead he offers a test that Bajie can verify with his own ears. It is the only argument in this chapter that anybody wins honestly.