原文 Original text
繁體 Traditional
Reader's edition
一股子黑氣 A Gout of Black Vapour
正自家這等誇念中間，忽然見林南下有一股子黑氣，骨都都的冒將上來。行者大驚道：「那黑氣裡必定有邪了。正自家这等夸念中间，忽然见林南下有一股子黑气，骨都都的冒将上来。行者大惊道：「那黑气里必定有邪了。
逐句解 Line by line
正自家這等誇念中間，忽然見林南下有一股子黑氣，骨都都的冒將上來。
正自家这等夸念中间，忽然见林南下有一股子黑气，骨都都的冒将上来。
In the middle of congratulating himself in this fashion, he suddenly saw, away to the south of the wood, a gout of black vapour come bubbling up.
骨都都 is a sound-and-motion word for something welling thickly up, read gǔ dū dū. It has no meaning apart from the noise it makes, and the doubled tail is what does the bubbling. English has nothing better than "glug."
行者大驚道：「那黑氣裡必定有邪了。
行者大惊道：「那黑气里必定有邪了。
Pilgrim was greatly alarmed and said, "There is certainly something evil in that black vapour.
邪 covers everything crooked, unlucky or possessed — nearer to "something wrong with it" than to any named class of monster.
The good cloud has a counterpart and it arrives the moment Pilgrim finishes admiring the good cloud. The novel almost never lets a character enjoy anything for longer than a paragraph.
The physics of this is worth noticing because it governs the whole chapter. Moral quality is visible from the air as coloured vapour: gold over the Tang Monk, black over whatever is south of the wood. Pilgrim is not guessing, and he is not being suspicious. He is looking at it.