白馬人言 The Horse Speaks
那白馬認得是八戒，忽然口吐人言，叫聲：「師兄。」這獃子嚇了一跌，扒起來，往外要走。被白馬探探身，一口咬住皂衣，道：「哥啊，你莫怕我。」八戒戰兢兢的道：「兄弟，你怎麼今日說起話來了？你但說話，必有大不祥之事。」那白马认得是八戒，忽然口吐人言，叫声：「师兄。」这呆子吓了一跌，扒起来，往外要走。被白马探探身，一口咬住皂衣，道：「哥啊，你莫怕我。」八戒战兢兢的道：「兄弟，你怎么今日说起话来了？你但说话，必有大不祥之事。」
逐句解 Line by line
The white horse, knowing him for Bajie, suddenly uttered human speech and cried: "Brother!"
認得 ("to recognize") takes 得 as de; 口吐人言 is "to spit forth human words." 那 is deictic nà. That the horse speaks at all is a marked event — the dragon-mount is silent through nearly the whole journey.
The blockhead started so he fell in a heap, scrambled up, and made to bolt outside.
嚇了一跌 ("started into a fall") and 扒起來 ("scrambled up") keep Bajie firmly in the comic register even at the moment of wonder.
But the white horse stretched forward and with one bite caught his black robe: "Brother, do not be afraid of me."
皂衣 is a "black robe"; 探探身 ("craned its body forward"). The horse must physically restrain the fleeing Bajie to be heard.
Trembling, Bajie said: "Little brother, how is it you’ve begun to talk today? If you speak, there must be some great calamity afoot."
戰兢兢 ("trembling, shaking"). Bajie’s instinct is sound even as his courage fails: a speaking horse portends disaster.
The horse’s breaking of silence is a genuinely marked moment. Through nearly the whole pilgrimage the dragon-prince serves mutely as Tripitaka’s mount; here, driven by the crisis, he speaks for the first time, and the very fact of his speech carries the weight of emergency. Bajie’s terror registers how unnatural, and how grave, the moment is.
The scene’s comedy and its urgency are finely balanced. Bajie tumbles and bolts; the horse must catch his robe in its teeth to hold him; and yet Bajie’s frightened intuition — that a speaking horse means "some great calamity" — is exactly right. The vernacular novel routinely lets its clown blunder into the truth.