During the Three Kingdoms period, the Wei general Sima Zhao seized control of the imperial court, arbitrarily deposing and killing emperors, and later proclaimed himself Duke of Jin and King of Jin. Just months after his death, his son Sima Yan usurped the Wei throne and declared himself Emperor Wu of Jin.
Man Fen, born into a distinguished family, along with his uncle Man Wei, had joined Sima Zhao's camp like many former Wei officials and earned his trust. But disaster struck when Man Wei's son offended Sima Zhao's brother, was tortured, and beaten to death, leading to Man Wei's dismissal from office. This tragedy haunted Man Fen, filling him with constant dread that calamity might strike at any moment, making him overly cautious in everything.
Man Fen was terrified of the wind. At the slightest breeze, he would refuse to leave his home, sealing every window and door, and even drawing the curtains tight. The mere howl of the wind would make his heart race and leave him unable to sit still.
Shortly after ascending the throne, Emperor Wu of Jin, Sima Yan, summoned his advisor Man Fen to the palace for a discussion. After paying his respects, Man Fen was directed to sit on a chair near the Beixia Gate window.
Man Fen noticed several semi-transparent glass screens by the north window. To him, they seemed like empty frames that couldn't block the wind. Outside, tree branches swayed violently in the gale. After sitting down, he grew visibly uneasy, repeatedly turning back to stare at them.
Emperor Wu of Jin had long heard that Man Fen was terrified of wind. Seeing his uneasy expression, the emperor smiled and asked, "Are you afraid of the wind?" Man Fen quickly rose and replied, "Yes, Your Majesty, the wind is strong, and I feel a bit cold." Emperor Wu laughed heartily and said, "There's no wind here! Look closely—the wind is outside. How could you feel cold?"
Man Fen stood up again, squinted, and looked closely—only to realize it was a translucent glass screen, and the wind outside couldn't possibly blow in. Blushing, he apologized to Emperor Wu of Jin, saying, "Your subject is like a Wu ox, panting at the sight of the moon. Please forgive my discourtesy, Your Majesty!"
The idiom "Wu Niu" refers to water buffalo from the Wu region south of the Yangtze River. These buffalo feared heat, spending summer days soaking in rivers or resting in shade, and were so terrified of the midday sun that they would pant heavily at the mere sight of it—some even mistook the moon at night for the sun and panted in fright. The Jin Dynasty official Man Fen suffered a similar phobia of wind, to the point that when he saw trees swaying outside, he would panic, convinced the wind was blowing directly on him.
Later generations used this story, coining the idiom "Wu Ox Panting at the Moon" to describe fear born from suspicion.
Source: *Fengsu Tongyi*, "Lost Texts"
Meaning of the Idiom: Later, the Chinese idiom "吴牛喘月" came to describe how fear born from suspicion.