蒼蠅兒 Changed into a Green Fly
若是這般去啊，他認得我了。且變化了去。」搖身捻訣，就變做個蒼蠅兒，輕輕的飛在門樓上聽聽。若是这般去啊，他认得我了。且变化了去。」摇身捻诀，就变做个苍蝇儿，轻轻的飞在门楼上听听。
逐句解 Line by line
"If I go in like this, they will know me."
The verb of recognising takes 得 as dé, the full reading fused onto a verb of perception rather than the light linking syllable. It is the same phrase Bajie used about the two water-carriers, and Pilgrim brushed it aside then.
"I had better change before I go."
Five characters, and the plan resolves itself. He has arrived at Bajie's objection and Bajie's solution, one scene later, on his own account.
He shook himself and made the sign, turned into a blue-bottle fly, and floated up lightly to perch on the gate-tower and listen.
蒼蠅 is the common housefly. Pilgrim has seventy-two transformations available and he picks the one that can sit on a roof beam for as long as it likes without anyone glancing at it. 捻訣 is to make the finger-sign that sets a spell going, the standard gesture before any change in this book.
Pilgrim ends up doing exactly what he told Bajie to do at the well, for exactly the reason Bajie gave. The novel does not point this out. It simply lets the pattern repeat, one rank up.
The choice of fly is the craft of the thing. A great deal of this novel's magic is spectacular, and the transformations that actually work are almost always the modest ones — a fly, a gnat, a peach. Pilgrim is at his most dangerous when he is at his smallest, and the chapter is about to prove it twice over.