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Yue Guang had a frequent guest in his brother-in-law, who used to call on him regularly but had failed to turn up for some time. When Yue asked the reason why, the man answered: "On my last visit, you kindly treated me to wine. Just as I was going to take a sip, I saw a snake wriggling in the goblet and I felt quite sick. Nevertheless, I drank; then I soon fell ill."

Now in those days it was a custom prevailing in Henan Prefecture for a prefect to have a bow painted to look like a snake and hung in his hall. Suspecting that the snake alluded to was nothing but a reflection of the decorated bow, he invited the man again for a drink and set the table in the usual spot.

"Do you still see something in the wine cup?" asked the host.

"Yes. Exactly as before," was the answer.

Then Yue Guang explained what he thought the whole trouble must have been. At that, the guest realized what had happened and instantly relieved of his obsession, and returned to normal.

Jinshu

樂廣嘗有親客，久闊不復來。廣問其故，答曰：「前在坐，蒙賜酒，方欲飲，見杯中有蛇，意甚惡之，既飲而疾。」於時河南廳事壁上有角弓，漆畫作蛇。廣意杯中蛇即角影也。復置酒於前處，謂客曰：「酒中復有所見不？」答曰：「所見如初。」廣乃告其所以。客豁然意解，沉痾頓癒。

《晉書‧樂廣傳》