He didn't know it until I put a bug in his ear.

我向他透露之后他才知道这件事。

----------------------------------------------------------------------
　　在put a bug in one's ear这个短语中，bug不是“虫子”的意思，而是“想法，消息”之类（idea, notion or information）。整个短语的意思就是，以微妙、慎重的方式向另一个人传递有用的信息（To impart useful information to (another) in a subtle, discreet way）。
　　例句：
　　I know you want to transferred to the sales department. I'll put a bug in the boss' ear for you.
　　我知道你想调到销售部去。我会往老板耳朵里吹吹风。