飛蛇掣電 Like Flying Snakes And Lightning
好獃子，就跳起雲頭，趕上就築。那怪物又使一條槍抵住。兩條槍就如飛蛇掣電。八戒誇獎道：「這妖精好槍法！不是山後槍，乃是纏絲槍；也不是馬家槍，卻叫做個軟柄槍。」好呆子，就跳起云头，赶上就筑。那怪物又使一条枪抵住。两条枪就如飞蛇掣电。八戒夸奖道：「这妖精好枪法！不是山后枪，乃是缠丝枪；也不是马家枪，却叫做个软柄枪。」
逐句解 Line by line
That fine idiot sprang up onto a cloud, came up with them and struck.
好獃子 answers 好行者 twelve segments earlier — the same storyteller's formula, handed to the other disciple.
The creature brought a second spear to bear and held him off.
又 marks this as an additional spear rather than the same one. The creature now has two in play, one for each opponent, which nobody stops to wonder about.
The two spears were like flying snakes, like lightning drawn.
掣電 is lightning pulled across the sky. The narrator says "snake" here, two hundred and thirty-three characters before the creature is revealed to be one, and nobody in the scene notices.
Eight Rules said admiringly, "This demon has a fine spear technique!
誇獎 is open praise — and it is being paid to the thing he came up to hit.
"It is not the Hill-Rear spear — it is the Winding-Silk; and it is not the Ma family spear either, but what you would call a soft-shafted spear."
Two halves of one sentence, cut by a semicolon and rejoined: 不是X，乃是Y against 也不是X，卻叫做個Y, ten characters against thirteen, the same formula at the same depth. The Hill-Rear and Ma-family spears are real named schools of Ming martial technique; the "soft-shafted spear" is not.
Eight Rules joins the fight and inside three segments he is appraising the enemy's technique. He went up to claim a share of the credit and has been sidetracked into connoisseurship.
The list of named styles is the third list he has produced in this chapter — after the beasts and goblins of the hills, and the three kinds of tie he does not have with the demon — and the only one that is technical. He knows what a Hill-Rear spear is and what the Ma family spear is, and he is confident this is neither.
The narrator's simile is doing quiet work in the background. Nobody in the scene has said the word "snake," and the creature will not be seen properly until daylight.