一毫虛的 Not One Hair Of Falsehood
老者道：「可老實麼？」八戒道：「我生平不敢有一毫虛的。」老者道：「你莫像才來的那個和尚走花溜水的胡纏。」八戒道：「我不像他。」老者道：「可老实么？」八戒道：「我生平不敢有一毫虚的。」老者道：「你莫像才来的那个和尚走花溜水的胡缠。」八戒道：「我不像他。」
逐句解 Line by line
The old man said, "Can you be honest about it?"
可老實麼 is the whole of the old man's remaining scepticism, and it is aimed at the right thing. He has been told two stories already.
Bajie said, "I have never in my life dared utter one hair of falsehood."
一毫 is one fine hair, the smallest unit of anything, and 生平 is in the whole course of a life. Bajie is swearing on his entire biography, which the reader knows a good deal about.
The old man said, "Do not be like that monk who came before, slipping and sliding about and talking nonsense."
走花溜水 is a marvellous phrase — walking on flowers and sliding on water, meaning slippery, evasive, not to be pinned down. 胡纏 is to tangle a person up in talk.
Bajie said, "I am not like him."
Seven characters, flat, with no elaboration at all — which after the flowers and water is the most convincing thing he could have said.
The old man has learned something from the first interview and is applying it. He does not ask whether the story will be true; he asks whether this one can manage honesty, which is a question about the witness rather than the evidence.
Bajie's oath is enormous and his final answer is tiny. Never in my life one hair of falsehood, and then, when pressed: I am not like him. The second sentence does all the work.
The phrase for his brother's manner is the keeper. Walking on flowers and sliding on water is precisely what Pilgrim did on this hillside — flattery, accusation, a boast about the kings of hell — and the old man has summed it up in four characters.