伸起頸來 One Of Them Put His Head Out
那些小怪在裡面，一個個嚌嚌嘈嘈，挨挨簇簇。中間有個大膽些的，伸起頸來，望洞外略看一看，一頭撞著個天兵，一聲嚷道：「在這裡！」那些小怪在里面，一个个哜哜嘈嘈，挨挨簇簇。中间有个大胆些的，伸起颈来，望洞外略看一看，一头撞着个天兵，一声嚷道：「在这里！」
逐句解 Line by line
Those little demons inside were chattering and clamouring, jostling and crowding together.
Four doubled pairs in eleven characters. 嚌嚌嘈嘈 is a rare one — a clamour of voices all at once — and 挨挨簇簇 is pressing and bunching. The novel is telling you the room is small by telling you how the bodies are arranged in it.
One in the middle, bolder than the rest, stretched his neck up and took a quick look outside the cave — and ran his head straight into a heavenly soldier. He let out a yell: "They are in here!"
The entire heavenly expedition succeeds because a small demon was curious. 撞著 puts 著 at zháo, the resultative — he did not merely bump, he got himself bumped into a soldier. 略看一看 is a quick look, with the verb doubled to make it brief, and 中 is zhōng, in the middle.
This is how the master is found: not by the cordon, not by the search, not by Pilgrim. A demon who could not resist looking pokes his head out and hits a soldier with it.
The novel has spent the whole chapter on plans — a plaint, a summons, an army, a coordinated assault — and resolves it with an accident. That is not carelessness. It is the same joke as the shoe.