變做天鵝 He Becomes A Swan
那老牛不得進洞，急抽身。又見八戒、行者趕來，慌得卸了盔甲，丟了鐵棍，搖身一變，變做一隻天鵝，望空飛走。那老牛不得进洞，急抽身。又见八戒、行者赶来，慌得卸了盔甲，丢了铁棍，摇身一变，变做一只天鹅，望空飞走。
逐句解 Line by line
The old bull could not get into the cave, and hurriedly drew back.
不得 takes the light linking de under a "can/cannot" frame, the same construction as 認不得 and 恨不得 earlier in the chapter. The tone settles without help, since 不 is bù before a rising tone and before an unstressed syllable alike.
Seeing Eight Rules and Pilgrim coming after him, he was so alarmed that he threw off his armour, dropped his iron staff, shook himself and changed into a swan, and flew away into the sky.
Armour off, staff dropped, shape changed, gone — and the order of the clauses is the point. 慌得 takes the light linking de, hooking the fright to everything that follows; this edition names 慌得推倒 as its example of the pattern. (一 shifts to yì in 一隻, before a level tone, and to yí in 一變, before a falling one.) The swan is the first transformation either party has used to escape rather than to deceive.
The Bull King's escape is stripped down item by item, and the order of the clauses is the point: armour off, staff dropped, shape changed, gone. He has now lost his mount, his armour and his weapons twice over in two chapters, and this time he sheds them himself in order to move.
The transformation is the first in the sequence used to flee rather than to deceive. Every earlier change of shape in these chapters has been an impersonation — the Great Sage as the Bull King, the Bull King as Eight Rules, the crab at the pool. A swan flying up out of a broken gate is only a way of leaving, and it opens the long transformation chase that the rest of the chapter is made of.