探骊得珠：《庄子·列御寇》上说，黄河边上有人泅入深水，得到一颗价值千金的珠子。他父亲说：“这样珍贵的珠子，一定是在万丈深渊的黑龙下巴底下取得，而且是在它睡时取得的。”后来用“探骊得珠”比喻做文章扣紧主题，抓住要领。

According to Zhuangzi·LieYukou, when a man dived into the depth of the Yellow River and obtained a priceless pearl, his father commented, "This kind of valuable pearl must have been obtained from underneath the jaw of the black dragon residing in a bottomless hole while the dragon was asleep." (fig.) probe deep and grasp the point of a themel; to the point (骊 li：黑龙 black dragon)