I presently perceived she was (what is vernacularly termed) trailing Mrs. Dent; that is, playing on her ignorance—her trail might be clever, but it was decidedly not good-natured.

我立刻意识到她（用白话来说）在跟踪丹特夫人；也就是说，利用她的无知——她的踪迹可能很聪明，但绝对不是善意的。