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)