莫說黑話 None of Your Dark Talk
那老母笑道：「轉不過去，轉不過去。只除是會飛的，就過去了。」八戒在傍邊賣嘴道：「媽媽兒莫說黑話，我們都是會飛的。」那老母笑道：「转不过去，转不过去。只除是会飞的，就过去了。」八戒在傍边卖嘴道：「妈妈儿莫说黑话，我们都是会飞的。」
逐句解 Line by line
The old woman laughed. "There is no going round it. No going round it.
The repetition is how spoken Chinese says absolutely not, and the novel writes it exactly as it would be said.
Unless you can fly. Then you would get past."
She means it as a figure of speech — the thing nobody can do. Given her audience it is an unusually badly chosen impossibility.
Bajie, standing to one side, ran his mouth. "Mother, none of your dark talk. We can all of us fly."
Bajie takes the impossibility literally and is, for once, right. 傍 is páng again, the side — he is standing off to one side, not keeping close to anything. 賣嘴 is to sell with the mouth, and it means showing off in talk, which is Bajie's whole character in two characters. 黑話 is dark talk, ordinarily thieves' cant or coded speech; here he is using it for gloomy talk, and telling an old lady to stop being morbid.
Three exchanges and the escape routes are gone. Round is impossible, through is fatal, and flying — which they genuinely can do — is about to be ruled out too, not by the old woman but by the rule this book holds to throughout: the master walks. Everything the disciples can do on their own is useless while he does.
Bajie's boast is also the chapter's first note of what actually saves them. He is wrong that flying is the answer and right that the answer is a trick. The solution when it comes will be transformation, disguise and theft — the disreputable half of the toolkit, not the heroic half.