一聲響亮 A Loud Ringing Knock
拿起來往石頭上一摜，噹的一聲響亮。沙和尚道：「哥哥，響哩。」行者道：「響便是個假的。我教他現出本相來你看。」拿起来往石头上一掼，当的一声响亮。沙和尚道：「哥哥，响哩。」行者道：「响便是个假的。我教他现出本相来你看。」
逐句解 Line by line
He picked it up and dashed it against a stone, and it went down with a loud ringing crack.
噹 is the noise itself, written with the mouth element to mark it as a sound — a clang, a knock on something hollow. The experiment takes fifteen characters and settles the question completely.
Sha Monk said, "Brother, it rang."
Eight characters from the quietest member of the party, and they are the ones that confirm the result. Sha Monk has almost no lines in this chapter and this is his best one — a plain report of what he heard.
Pilgrim said, "If it rang, it is a fake.
The logic is stated as a single clean conditional. Ring, therefore hollow; hollow, therefore not a head. Nothing in the chain requires any power at all.
Let me make it show its true form and you shall see."
現出本相, to make something show its original form, is the novel's standard phrase for stripping a disguise, and it usually applies to a shapeshifter. Wukong is about to apply it to a piece of firewood, which is a small joke: the object has no true form to reveal, only a material.
The experiment is a proper one — hypothesis, prediction, test, independent confirmation from a third party. Sha Monk saying it rang is the peer review.
The phrase about showing a true form is doing double duty. It is the vocabulary of magic, used dozens of times in this book when a monster is beaten back into its animal shape, and here it is being used for a plain act of smashing. The prop has no secret self. It is just wood, and one blow will say so.