要蒸是要煮 Steamed or Boiled
八戒道：「師父在裡邊受罪哩，綁著是綑著？要蒸是要煮？」行者道：「這個事倒沒有，只是安排素宴，要與他幹那個事哩。」八戒道：「师父在里边受罪哩，绑着是捆着？要蒸是要煮？」行者道：「这个事倒没有，只是安排素宴，要与他干那个事哩。」
逐句解 Line by line
Bajie said, "The master is inside suffering, is he? Tied up, or trussed?"
Both characters for binding take 著 as zhe, the reading for a state held in place — not tied once but sitting there tied. 綁 is to bind with rope and 綑 is to bundle up, and the pair is asking about degree rather than method.
"To be steamed, or to be boiled?"
Five characters, and they are the standard fate of a captive in this book. Bajie has gone straight to the cooking, because that is what happens to travellers who fall into caves.
Pilgrim said, "There is nothing of that sort. It is only that she has laid on a plain banquet, and means to do that business with him."
The evasion is delicate and slightly embarrassed. 倒 is dào, the on-the-contrary reading, and 那個事 — that business — is Pilgrim declining to name it in front of the other two. He was blunter about it with Tripitaka.
Bajie's questions are the questions of somebody who has read this story before. Tied or trussed, steamed or boiled — these are the standing options for a captured pilgrim, and the novel has used them many times.
Which is exactly why the answer lands. None of the usual apparatus applies. Nobody is being cooked; there is a dinner party and a wedding, and Pilgrim has to explain it in euphemism to a pig standing in a field.