鴨蛋粗細 Thick as a Duck Egg
行者暗喜，才跳下來，現出本相。耳朵裡取出棒來，幌一幌，有鴨蛋粗細，噹的一聲，把旁門打破，跑至後園，高叫：「師父！」行者暗喜，才跳下来，现出本相。耳朵里取出棒来，幌一幌，有鸭蛋粗细，当的一声，把旁门打破，跑至后园，高叫：「师父！」
逐句解 Line by line
Pilgrim was secretly delighted. Only then did he drop down and show his true form.
Twelve characters. He has been an ant on a roof-beam through an entire council meeting, and the household is now asleep, so the disguise has done its work.
He took the rod out of his ear, gave it a flourish until it was as thick as a duck's egg, and with a clang smashed the side door open, ran to the back garden and called loudly, "Master!"
The rod lives in his ear at needle size and comes out at whatever thickness he wants — 耳朵, an ear, is a phrase whose second character takes an unstressed ending. A duck's egg is a domestic measure, the sort of thing you would use to describe a rolling pin. 噹 is the clang itself, and it is the same sound word the false head made when it hit the stone.
The whole cave is asleep, so Wukong stops being careful. He goes from an insect on a beam to a monkey with an iron bar in the space of one sentence.
Sizing the rod against a duck's egg is very much this novel's way with the marvellous. A weapon that grows and shrinks at will, weighing thousands of catties, gets its measure from something on the kitchen shelf.