劈做兩半 The Head Splits In Two
那老魔舉刀又砍，大聖把頭迎一迎，乒乓的劈做兩半個。大聖就地打個滾，變做兩個身子。那妖一見慌了，手按下鋼刀。那老魔举刀又砍，大圣把头迎一迎，乒乓的劈做两半个。大圣就地打个滚，变做两个身子。那妖一见慌了，手按下钢刀。
逐句解 Line by line
The old fiend raised the sabre and chopped again. The Great Sage gave his head a tip to meet it, and with a bang it split into two halves.
乒乓 — the same noise-pair that banged the cave doors shut earlier in the chapter, and the one that eventually gave Chinese its word for table tennis. The head does split; the poem never claimed it would not.
The Great Sage rolled on the ground and became two bodies.
Eleven characters to turn a fatal wound into a doubling. The transformation is not explained and does not need to be — a reader seventy chapters in knows that rolling on the ground is how this creature changes shape.
The demon panicked at the sight and let his steel sabre drop.
手按下, the hand pressing it down — not thrown away, lowered. He has stopped fighting without deciding to.
This is the pivot the whole three-cut wager was built for. The demon's poem promised that one slice makes two gourd-dippers; the slice lands, and it makes two Sun Wukongs. The book lets the boast come true in the most literal and least useful way possible.
The economy of it is worth admiring. Three sentences, no commentary, no explanation of the magic — a bang, a roll, two of him, and a demon lowering his weapon. Everything the chapter has spent on poems it saves here.