How do you know that? 你怎么知道

434. That's why they came back.
     所以回来了
435. That's why their eyes turned blue.
     而眼睛也变蓝了
436. Only fire will stop them.
     只有用火烧才能阻止他们
437. How do you know that?
     你怎么知道
438. I read about it in a book...
     我在书上看到的
439. a very old book in Maester Aemon's library.
     伊蒙学士的图书室里有一本非常古老的书
440. What else did the book say?
     书上还说了什么

来自《权力的游戏 第一季 第八集 Game of Thrones S01E08 奈德性命堪忧》第 437 行