荊棘丫叉 Thorns Above The Path
三藏勒馬觀看，那嶺上荊棘丫叉，薜蘿牽繞，雖是有道路的痕跡，左右卻都是荊刺棘針。唐僧叫：「徒弟，這路怎生走得？」行者道：「怎麼走不得？」又道：「徒弟啊，路痕在下，荊棘在上，只除是蛇蟲伏地而遊，方可去了；若你們走，腰也難伸，教我如何乘馬？」三藏勒马观看，那岭上荆棘丫叉，薜萝牵绕，虽是有道路的痕迹，左右却都是荆刺棘针。唐僧叫：「徒弟，这路怎生走得？」行者道：「怎么走不得？」又道：「徒弟啊，路痕在下，荆棘在上，只除是蛇虫伏地而游，方可去了；若你们走，腰也难伸，教我如何乘马？」
逐句解 Line by line
Tripitaka reined in his horse to look. On that ridge the brambles forked and crossed and the creepers twined and trailed; and though there was some trace of a path, to left and right there was nothing but thorn and spine.
勒 at lè is reining a horse in by the bit; the automatic reading gives lēi, which is tightening a cord round something. 跡 is read jì, the modern standard, against the automatic jī — the character runs exactly parallel to 績, which the corpus already holds at jì for the same reason, and it has been registered here so the reading no longer depends on one passage remembering it.
The Tang Monk called out, "Disciples, how is this road to be walked?"
怎生 sets up a question about whether something can be done, and the 得 after it links rather than heads a clause of its own, so it takes the light de.
Pilgrim said, "Why should it not be walked?"
Pilgrim's whole answer is to repeat the question back. The negative 不得 always links, so 得 is light here. The tone rule computes 不 against the underlying tone of what follows and reaches bù; the ruling that lightens 得 leaves that answer standing, so nothing needs overriding.
He spoke again: "Disciple! The trace of the path lies below and the brambles above. Unless one were a snake or a worm, to crawl belly-down along the ground and so pass through, there is no getting by;
The Tang Monk is speaking again, picking up after Pilgrim's interruption — the address 徒弟啊 and the question about riding in the next breath both fix it as his. The unit stops at a semicolon with the quotation still open.
"and if you were to walk it you could not so much as straighten your backs. How then am I to ride?"
乘 at chéng is to ride or mount; the shèng band, which counts chariots as units, is not in play. 教 is the causative jiào, "cause me to", which English turns into the exasperated "how then am I to".
The description of the ridge is built out of paired verbs — forking and crossing, twining and trailing — and it ends on the flat observation that there is a trace of a path and nothing on either side of it but thorns. The trace is the trap. A ridge with no road at all could be avoided; a ridge with the suggestion of a road invites the attempt.
Tripitaka's objection is precise and physical. He does not say the ridge cannot be crossed; he says the path runs underneath the brambles, so that anything going along it has to go belly-down. His image is a snake or a worm, and the sting is in the arithmetic that follows: even his disciples would have to stoop, and he is on a horse.
Pilgrim's one-line retort — why should it not be walked? — is the reflex of a creature terrain has never stopped. It is also, for once, the wrong instinct, and the chapter knows it. This obstacle will not yield to leaping or to strength of arm, and the disciple who solves it is not Pilgrim.