隨機答應 I Shall Answer As It Comes
卻又自揣自度道：「老孫變作小鑽風，這一進去，那老魔若問我巡山的話，我必隨機答應。倘或一時言語差訛，認得我啊，怎生脫體？却又自揣自度道：「老孙变作小钻风，这一进去，那老魔若问我巡山的话，我必随机答应。倘或一时言语差讹，认得我啊，怎生脱体？
逐句解 Line by line
But then he weighed it up and reckoned it over with himself. "Old Sun has turned into a Little Borer of the Wind, and once I go in, if the old demon questions me about patrolling the mountain I shall have to answer as the moment requires.
自揣自度 is to weigh and to reckon, both verbs of estimating, and 度 is duó here — the base offers the noun reading instead, though it managed duó unaided at the same compound earlier in the chapter. 隨機答應 is to answer as the occasion turns, with 應 as yìng.
And if a word should go wrong at some point and he knows me — how am I to get my body out of it?"
差訛 is a slip or discrepancy; the character takes chā in this noun sense, as it does in the ordinary modern word for an error, rather than the chà of being wrong that it took a passage ago. 認得 keeps 得 as dé, the perception suffix — while its own negative took the unstressed reading earlier in the chapter. 脫體 is to get the body out, to extricate oneself.
Having counted the army, Pilgrim immediately stops thinking about it and starts thinking about conversation. The danger he identifies is not the ten thousand spears; it is being asked a question he cannot answer.
That is a fair assessment. He has already come within one sentence of exposure this afternoon, when a demon asked him something an officer would know.
And the phrase for his worry is precise. How am I to get my body out — not escape, not fight, but extract the physical self from a place he has walked into on purpose.