做些鮮湯 Fish To Make A Broth
好獃子，真個收了鈀，一家一個，都抓下塔來。那怪只叫：「饒命。」八戒道：「正要你鮎魚、黑魚做些鮮湯，與那負冤屈的和尚吃哩。」好呆子，真个收了钯，一家一个，都抓下塔来。那怪只叫：「饶命。」八戒道：「正要你鲇鱼、黑鱼做些鲜汤，与那负冤屈的和尚吃哩。」
逐句解 Line by line
Good Idiot! He did indeed put up his rake, and they took one apiece and carried them down out of the pagoda.
好獃子, Good Idiot, is the storyteller's exclamation used for Eight Rules exactly as 好猴王 was used for Pilgrim on the roof. 一家一個 is one to each household, here one prisoner to each captor; the first 一 stays yì before a level tone and the second falls to yí before 個.
The fiends only cried, "Spare us!"
This is the third moment in the chapter at which they cry 饒命, spare us — on the roof, at the start of the confession, and now on the stairs — and the fourth time the words are actually said, since they doubled it the first time.
Eight Rules said, "It is precisely you catfish and black fish I want, to make a little fresh broth for those wronged monks to eat."
The joke turns on the confession itself. They named their own species under interrogation, and Eight Rules has been listening to a deposition as though it were a fishmonger's slab. 鮮湯 is fish soup, and 鮮 is written with the fish radical in it.
The chapter lets Eight Rules have the last word and it is a joke about dinner. The two fiends have just given the deposition that will free a monastery, and what he takes away from it is that a catfish and a black fish would make good soup for the monks who have been in cangues.
It is crueller than it looks and the novel means it to be. The creatures are being carried down a pagoda in the middle of the night crying for their lives, and the pig is working out a recipe over their heads. Nobody corrects him.