講開馱法 Setting Terms for the Carrying
行者聞言道：「這廝造化哩，我那師父是個慈悲好善之人，又有些外好裡枒槎。我待不馱你，他就怪我。馱便馱，須要與你講開：若是大小便，先和我說；若在脊梁上淋下來，臊氣不堪，且污了我的衣服，沒人漿洗。」那怪道：「我這般一把子年紀，豈不知你的話說？」行者才拉將起來，背在身上，同長老、沙僧，奔大路西行。那山上高低不平之處，行者留心慢走，讓唐僧前去。行者闻言道：「这厮造化哩，我那师父是个慈悲好善之人，又有些外好里枒槎。我待不驮你，他就怪我。驮便驮，须要与你讲开：若是大小便，先和我说；若在脊梁上淋下来，臊气不堪，且污了我的衣服，没人浆洗。」那怪道：「我这般一把子年纪，岂不知你的话说？」行者才拉将起来，背在身上，同长老、沙僧，奔大路西行。那山上高低不平之处，行者留心慢走，让唐僧前去。
逐句解 Line by line
Pilgrim, hearing this, said: "This creature's in luck! That master of mine is a merciful, good-hearted man — though smooth without, he's a bit gnarled and prickly within.
造化 (zào huà) means "creation" in a philosophical text and "a stroke of luck" in a spoken one; this is the spoken one. 外好裡枒槎 (wài hǎo lǐ yā chá) is the sharpest thumbnail portrait of Tripitaka anywhere in the book: 枒槎 is the snags and forks of rough timber, so the master is smooth-planed on the outside and full of splinters within.
"If I were minded not to carry you, he'd only blame me for it."
待 (dài) here is "to be minded to, to be about to." 怪 (guài), "to blame." Pilgrim submits to the job purely to avoid a scolding, which tells you what he is actually afraid of.
"Carry you I will — but let's have it clear between us: if you need to relieve yourself, tell me first; should it run down my spine, the stink would be past bearing, and it'd foul my clothes with no one to wash them."
講開 (jiǎng kāi), "to talk a thing out and settle it plainly." 大小便 (dà xiǎo biàn) is the polite compound for relieving oneself, greater and lesser. 臊氣不堪 (sāo qì bù kān), "a stench past bearing." Pilgrim answers the demon's counterfeit dignity with the one register it cannot survive.
The fiend said: "A man of my years — do you think I don't know how to behave?"
一把子年紀 (yì bǎ zi nián jì), "a fair handful of years," is a colloquial way of claiming age; 把 is the measure word bǎ, and 一 accordingly yì. 豈不知 (qǐ bù zhī), "how could I not know" -- the demon standing on his dignity, which is the joke.
Only then did Pilgrim haul him up, hoist him onto his back, and with the Elder and Sha Monk make west along the high road.
拉將起來 (lā jiāng qǐ lái), "hauled him upright," 將 once more the small particle of motion. 背在身上 (bēi zài shēn shàng), "onto his back" -- 背 read bēi, the verb, not bèi, the noun for the back itself.
On the mountain's rough and uneven stretches, Pilgrim walked slowly and watchfully, letting Tripitaka go on ahead.
高低不平 (gāo dī bù píng), "rough going, all ups and downs." 留心慢走 (liú xīn màn zǒu), "to go slow and watch his step." He is not being careful. He is falling behind on purpose.
Resigned to the job, Pilgrim deflates the whole solemn performance with a run of coarse comedy, warning the venerable Daoist to give notice before relieving himself lest the results run down his spine and foul robes that nobody will wash. It is exactly his method -- meet counterfeit dignity with earthy specifics -- and his aside on the master, smooth outside and full of splinters within, is one of the best short character sketches in the book.
The passage closes the disguise sequence and starts the next one. Pilgrim shoulders the fiend, and on the rough ground he deliberately drops back and lets Tripitaka ride ahead -- the separation Sha Monk foresaw and the opening the demon has been engineering since he first lay down beside the road. The joke about the carrying-terms gives way, in the last image, to a small silence: one figure walking slowly at the rear with a monster on his back.