上門的買賣 Business That Walks In
那長老掙著要走，那女子攔住門，怎麼肯放，俱道：「上門的買賣，倒不好做。『放了屁兒，卻使手掩。』你往那裡去？」那长老挣着要走，那女子拦住门，怎么肯放，俱道：「上门的买卖，倒不好做。『放了屁儿，却使手掩。』你往那里去？」
逐句解 Line by line
The Elder struggled to get away, but the women barred the door — as if they would let him out. They all said, "Business that walks in at your own door is not to be turned down."
著 is zhe, the durative marker — struggling, keeping it up. 倒 is dào, the reversing adverb: on the contrary, it would be bad business to refuse. And the mask is off. One passage ago he was a guest; here he is stock that delivered itself.
"You have let the fart out; no use clapping your hand over it now."
A crude proverb, and deliberately so. 兒 takes the full ér on 屁兒. The sense is that a thing already done cannot be covered up — the same idea as the cat being out of the bag, delivered with none of the dignity anybody has been maintaining until now.
"Where do you think you are going?"
那 is nà — where. Five characters, and the courtesy that has held this scene together for six passages is gone completely.
The turn happens inside a single sentence. He pulls for the door, they block it, and the word they use for him is stock — business that has walked in by itself.
The proverb is the marker. Everything up to this point has been conducted in the elevated register of hospitality and merit — treasure-country, almsgiver's mansion, the perfection of giving. Then somebody says a sentence about farting, and you can hear the performance stop.
It is worth noticing that they never do drop the logic of the exchange. He is still a transaction: goods, a deal, a bad piece of business to refuse. They have simply changed which side of the table he is on. Fifteen passages of courtesy, and it ends in a sentence about wind.