In the Southern and Northern Dynasties Period (nán běi cháo 南北朝,420-589AD), there was a painter called Zhang Sengyou (zhāng sēng yóu 张僧繇). Once he visited a temple and painted on the wall four dragons, but gave none of them eyes. The onlookers felt that this was odd, and asked why he had not painted the eyes. He answered, ‘Eyes are crucial for dragons. With the eyes painted on , the dragons would fly away.’ Nobody believed this, so Zhang Zengyou took up his brush and added eyes to two of the dragons. No sooner had he finished than the two dragons flew into the sky amid a thunderstorm. The two without eyes stayed painted on the wall. This idiom is used to describe how, when writing or speaking, one or two key sentences will enhance the contents.