Literal Meaning: Groping about the chin of the black dragon to get a pearl
Metaphorical Meaning: Now it is used to indicate that the article is sufficient in meaning, concise in language and to the point.

Long, Long ago, there lived a family by the Yellow River. They lived a very poor life depending on cutting reeds, weaving hanging screens and dustpans for a livelihood. 

One day, the son was cutting reeds by the riverside. With the scorching sun directly overhead, his head was swimming, so he sat down to take a rest. Looking at the river water in front which was his father had once told him. in the depths of the river there were a lot rare treasures, but nobody dared to get them because a fierce black dragon was residing there. He thought that, if he could dive into the depth of the river and get the treasures, the whole family would mot have to toil from morning till night and yet could mot have enough to eat as now. He thought it would be better to have a try, and he was resolved to try in desperation. So he took off his clothes nimbly and dived into the cold water with a splash. 

At first, he could see small fish here and there all around. However, the deeper he dived , the darker it became, and the colder the river water. At last, it was pitch-dark all around, and he could see nothing. He became frightened, and was at a loss where he should swim to. Just at that time, he noticed a round object which was glittering not far away.  He fixed his eyes on it, and saw it was a bright pearl.  He held his breath and swam over there, held the pearl with both hands, pulled it with a great effort, and the bright pearl come into his arms. He came out from the water immediately, climbed up the bank, and made off for home at once. 

His father saw the bright pearl, and asked where he had got it. He told his father the whole story exactly as it had happened. Hearing this, his father said repeatedly: “How dangerous it was! This precious pearl was grown on the chin of the black dragon. The black must have been sleeping when you were pulling the pearl. If the black dragon were awake, you would be dead. “When the son heard this, he considered himself very lucky indeed.