let sleeping dogs lie said to warn someone that they should not talk about a bad situation that most people have forgotten about 过去的事就让它过去吧;不要再去揭伤疤 A: Should I ask the boss if he's upset at my coming in late in the mornings? 我应不应该问老板他是不是对我早上迟到感到不高兴? B: If he hasn't said anything about it, just let sleeping dogs lie. 如果他什么也没说，那就让过去的事过去吧。