頓然省悟 The Bull King Understands
早間賢友著人邀我時，有個孫悟空保唐僧取經，路遇火焰山難過，曾問我求借芭蕉扇。我不曾與他，他和我賭鬥一場，未分勝負。我卻丟了他，徑赴盛會。那猴子千般伶俐，萬樣機關，斷乎是那廝變作蟹精，來此打探消息，偷了我獸，去山妻處騙了那一把芭蕉扇兒也。」早间贤友着人邀我时，有个孙悟空保唐僧取经，路遇火焰山难过，曾问我求借芭蕉扇。我不曾与他，他和我赌斗一场，未分胜负。我却丢了他，径赴盛会。那猴子千般伶俐，万样机关，断乎是那厮变作蟹精，来此打探消息，偷了我兽，去山妻处骗了那一把芭蕉扇儿也。」
逐句解 Line by line
"This morning, when my worthy friend sent a man to invite me, there was one Sun Wukong escorting a Tang Monk to fetch scriptures, whose road was blocked at the Mountain of Flames; and he asked me to lend him the banana-leaf fan."
著 is the causative zhuó — he sent a man — not the continuous reading. 間 is jiān and 難 is nán. He starts his reconstruction from the invitation that brought him here, which is also where the Great Sage's trail begins.
"I would not give it him, and he and I fought a bout together without deciding the victory."
分 is fēn in 未分勝負 — the same phrase the narration used of the duel itself. His account of the fight is exact and claims no advantage for either side.
"I left him standing and came straight to the noble gathering."
盛 is shèng, of a splendid occasion. 丟 is blunt: he dropped the man. We know the Great Sage was left standing on a peak waiting for him to come back.
"That monkey has a thousand kinds of cleverness and ten thousand sorts of contrivance. Beyond doubt it was that fellow who turned himself into the crab spirit, came here to spy out news, stole my beast, and has gone to my mountain wife's place to cheat her out of that banana-leaf fan."
All three instances of 那 here are the pointing kind. 兒 in 扇兒 is the swallowed suffix er. His reconstruction is complete and entirely correct, arrived at from one sentence of testimony.
The Bull King's reasoning is the best piece of thinking anybody does in this chapter, and the novel gives it to him in full. From the single fact that a crab spirit was present he reconstructs the transformation, the purpose, the theft of the mount and the errand it was stolen for — and he is right in every particular, including the one he cannot possibly have evidence for, that the fan has already changed hands.
What makes it possible is that he alone holds all the pieces. He fought the Great Sage that morning over this very fan; he knows the man's reputation for shapes; he knows where his own wife keeps house and what she has in it. The Dragon King's court could not have solved this and the Rākṣasī could not have seen it coming. Only the husband, who has been the object of the entire intrigue, can put it together.
It is worth noticing what the recognition costs him. He has spent the chapter being manoeuvred — invited away from a duel, impersonated at his own door, robbed through his abandoned wife — and the moment he finally understands the shape of it is also the moment he learns that his household has been the instrument.