This is the hinge of the chapter, and the novel puts it inside Wukong's head so that we can watch the trap close. He agrees with the demon. That is the remarkable part. He knows exactly what he could do from where he stands, he knows it would work, and he gives it up anyway, because the one thing he will not spend is his reputation.

The novel has been building this weakness since the opening chapters, and it is consistent: Wukong can be beaten by force only rarely, but he can be talked out of a winning position by anyone willing to question whether he is the figure he claims to be. It is the same lever that got him into trouble in Heaven. Here a demon he has never fought works it on the first attempt.

The resigned phrase he settles on — very well then, doubled — is the sound of a man talking himself into something he suspects is a mistake. He will reach for the same doubled phrase again before he leaves the belly, and both times it marks the point where he stops calculating and starts performing. The repetition is not carelessness on the author's part; it is a tic.