長了三五寸 Three Or Five Cun Taller
好大聖，你道他怎麼去問？跳下他的帽子來，釘在樹頭上，讓那小妖先行幾步。急轉身騰那，也變做個小妖兒，照依他敲著梆，搖著鈴，掮著旗，一般衣服，只是比他略長了三五寸，口裡也那般念著。好大圣，你道他怎么去问？跳下他的帽子来，钉在树头上，让那小妖先行几步。急转身腾那，也变做个小妖儿，照依他敲着梆，摇着铃，掮着旗，一般衣服，只是比他略长了三五寸，口里也那般念着。
逐句解 Line by line
Splendid Great Sage — and how do you suppose he went about questioning him?
你道 is the storyteller turning to the audience: and how do you think? It is the seam where a performance asks a question it means to answer itself.
He jumped down off the cap, pinned himself to a treetop and let the little demon go a few paces ahead.
釘在樹頭上 is to nail oneself to the treetop — the verb for driving a nail, used of a fly settling. Letting the mark walk on first is the oldest trick in surveillance.
Then he turned quickly, shifted his shape and became a little demon himself, beating a clapper and shaking a bell and shouldering a banner just as the other did, in the same clothes, only three to five cùn taller than him, chanting the same words.
騰那 is to vault and shift, and 那 is nuó in it — nothing in the authoring machinery consults the table that carries this, so it has to be forced by hand every time. Four more durative 著. And 略長了三五寸 is the detail that makes the disguise real: a 寸 is about three centimetres, so he is a hand's breadth too tall — close enough to pass and wrong enough to be noticed.
The impersonation is built by copying, item by item, off a man walking away from him. Clapper, bell, banner, clothes, and the words he is muttering.
The height is the flaw and it is put in deliberately. Three to five cùn is about a hand's breadth, which is nothing on a creature nearly four metres tall and is exactly the sort of thing a colleague notices.
This is Venus's advice being taken. Shifting, transforming, quickness, stratagem — not one blow struck, and the interrogation about to be conducted from inside the organisation.