Mistaking the Reflection of a Bow for a Snake

In the Jin Dynasty(265-420), a man called Yue Guang once invited a friend to have a drink at his home. When the friend lifted his cup, he saw a small snake in the wine, yet he forced himself to drink. Back home, the friend recalled the incident, and felt so disgusted that he fell ill. Hearing about this, Yue Guang invited his friend again. He asked him to sit in the same place and drink. Then his friend saw that the image of the snake in the cup was actually the reflection of a bow hung on the wall. Realising this, the friend recovered quickly. 

晋朝（公元265–420）时，有一个叫乐广的人，请他的朋友到家里喝酒。朋友端起酒杯喝酒的时候，忽然看见杯子里面有条小蛇的影子，他当时勉强将酒喝下。而回家后总是想起这件令人恶心的事，以至于生了病。乐广知道后，就把朋友再次请来，还是坐在原来的地方喝酒。那位朋友这才弄明白了，原来杯中的蛇影，是墙上挂着的一张弓映照出来的。事情弄明白了，病也就好了。 

This idiom indicates a condition of being over suspicious bringing trouble on oneself.

这个成语比喻疑神疑鬼，自相惊扰。