mistaking a shadow of a bow in the cup as a snake-beset with imaginary fears

According to History of fin Biography of Yue Guang， once a county magistrate， Yue Guang invited his secretary， Du Xing to dinner at his home. There was a red bow hanging on the north wall of Yuc's dining room and its shadow was just reflected in Du's wine cup. Du misunderstood the shadow as a snake. Although he was very frightened， he dared not turn down his superior's offer， and he had to swallow this wine with his eyes closed. After he went back， he fell sick at once. Knowing this fact， Yue Guang invited Du Xing to dinner again. Yue offered him still sitting in his original seat， then the shadow like snake was reflected in Du's cup as before. Yue pointed the shadow and said:\"The snake in your cup is nothing but the reflcetion of the red bow on the north wall.\" Hearing this， Du's illness disappeared at once.

From this story comes the idiom: \"Bei Gong She Ying\"--mistaking the shadow of a bow in a cup as a snake.

Now we usually use it to describe that one is terribly suspicious and creates disturbance within his ranks.

據(jù)《晉書·樂廣傳》記載，一次，州官樂廣請他的師爺杜興在他家吃飯。在他家廳堂的北墻上掛了一張紅弓，影子正好倒映在杜興的酒杯中。杜興誤以為那是一條蛇的影子，但又不敢拒絕喝他上級所敬的酒，就強忍著把酒喝下。他回家后立即病倒了。

樂廣了解此事后，于是又請杜興來飲酒，仍讓他坐在原來的坐位上，那張弓的影子又映在杜興的酒杯里。樂廣說：“這不過是北墻上紅弓的影子而已，哪有什么蛇?。　倍排d聽后，疑慮消失，病全好了。

由此故事，引來“杯弓蛇影”這個成語。后多用此形容某人疑神疑鬼，自相驚擾。