海闊從魚躍 Wide Sea and Empty Sky
諕得個三藏跳下馬來，打個問訊道：「老菩薩，古人云：『海闊從魚躍，天空任鳥飛。』怎麼西進便沒路了？」諕得个三藏跳下马来，打个问讯道：「老菩萨，古人云：『海阔从鱼跃，天空任鸟飞。』怎么西进便没路了？」
逐句解 Line by line
That gave Tripitaka such a fright that he sprang down from the horse and made his greeting, saying: "Venerable Bodhisattva, the ancients said, 'The sea is wide, so fish leap as they please; the sky is empty, so birds fly where they will.'
Tripitaka's reflex under fright is to be polite and quote something. 諕 is xià, to frighten, a variant of the character modern Chinese writes 嚇. The saying he reaches for is still current — it is the one Chinese uses for having room to move and nobody stopping you, which makes it a slightly comic thing to produce when someone has just told you the road ahead is fatal. And 老菩薩, Venerable Bodhisattva, is only a courteous way to address an old woman. He has no idea how right he is.
How can it be that going west there is no road at all?"
The question follows straight from the quotation: if the sky is wide enough for any bird, how can a road be closed? He is arguing from a proverb against an eyewitness.
This is the closest the novel comes to a running joke about Tripitaka: confronted with a fact, he produces a sentiment. His two lines about fish and birds are about freedom of movement in the abstract, and the old woman has just made a concrete claim about one specific road.
The bow he makes is the palms-together greeting a monk gives on meeting. He performs it correctly to a stranger by the roadside, and it happens to be the correct greeting for the Bodhisattva she actually is. The accident is the point — Tripitaka is courteous to exactly the degree the situation secretly deserves, and for none of the right reasons.