做個樁兒 Three Cuts At The Bald Head
老魔道：「你過來，先與我做個樁兒，讓我盡力氣著光頭砍上三刀，就讓你唐僧過去；假若禁不得，快送你唐僧來，與我做一頓下飯。」老魔道：「你过来，先与我做个桩儿，让我尽力气着光头砍上三刀，就让你唐僧过去；假若禁不得，快送你唐僧来，与我做一顿下饭。」
逐句解 Line by line
The old fiend said, "Come here and stand for me like a post first. Let me put my whole strength into three cuts at that bald head of yours, and I will let your Tang monk pass;
樁兒 is a stake driven into the ground — the demon is asking him to stand still and be a chopping stump. 著光頭 takes the light zhe, aiming the blow at a place.
"and if you cannot bear it, then bring your Tang monk along smartly and let him make me a meal."
禁 is jīn, to endure — not the jìn of forbidding. It is the same reading as the 難禁 of the fire dragons in the bottle, and the opposite of the one an earlier chapter uses for parents unable to restrain a son. 下飯 is what goes with the rice — a dish, a side. He is offering to eat the monk as an accompaniment.
The bargain is grotesque and completely serious. Three free cuts at a stationary head, and the pilgrimage passes or ends on the result. It is the kind of wager that only works in a book where one party has an indestructible skull, which is precisely why Wukong is about to accept with enthusiasm.
下飯 is the detail that gives the passage its edge. Not a feast, not a sacrifice — a side dish to go with rice. The demon has spent two chapters organising a conspiracy to obtain the holiest man on the road, and he thinks of him as something to put on the table beside the staple.