幾曾吃他 When Did Anyone Eat Him
大鵬咬著牙恨道：「潑猴頭！尋這等狠人困我。你那老和尚幾曾吃他？如今在那錦香亭鐵櫃裡不是？」大鹏咬着牙恨道：「泼猴头！寻这等狠人困我。你那老和尚几曾吃他？如今在那锦香亭铁柜里不是？」
逐句解 Line by line
The roc ground his teeth and said in his hatred, "You villainous monkey-head!"
著 in 咬著 is zhe, the teeth set and held so — the same reading as when the old fiend took Bajie by the scruff earlier in the chapter.
"Going and finding vicious people like this to trap me.
Seven characters of pure grievance. His complaint is that Wukong fetched somebody bigger, which has been every villain's complaint about him since Heaven.
When did anybody ever eat that old monk of yours?
幾曾 is when ever — a rhetorical question expecting the answer never. Nine characters, and the chapter's central lie collapses in them.
Is he not this moment in the iron chest in the Pavilion of Brocade Fragrance?"
The truth arrives out of spite. The roc is not confessing and not relenting; he is trying to hurt the monkey who beat him, and the only weapon left is a fact.
The rumour dies in four sentences and it is killed by malice. The roc has lost everything and gives up the master's hiding place purely to spoil somebody else's grief.
Look at what the reader has been carrying since the middle of the chapter. Two bound brothers repeating a lie in good faith, a lament, a flight to Vulture Peak, a resignation offered to the Buddha — all of it built on a story a frightened city was told, and all of it dispelled by a spiteful bird in nine characters.
And it comes from the one character in the chapter who never lied. The three fiends invented the rumour; the roc, cornered and furious, tells the truth because the truth is the cruellest thing available to him.