A young and beautiful wife fell gravely ill. On her deathbed, she made her husband promise never to remarry, threatening, "If you marry another, I will return as a ghost and make you suffer eternally!" The husband, respecting her wish, initially had no intention of remarrying.
However, merely three months after her funeral, he met another woman—younger, charming, and wealthy—who loved him deeply. He soon became engaged to her. That very night, the ghost of his late wife appeared, scolding him relentlessly for breaking his promise. To his terror, the ghost knew every detail of his interactions with his new fiancée.
Haunted and unable to eat or sleep, the desperate husband sought help from a Zen master. The master advised him, "The ghost knows all, but there is one thing she cannot know. Next time she appears, take a handful of mung beans and ask her how many are in your hand. If she cannot answer, you will know she is merely an illusion born of your own fear and guilt, and she will vanish."
The following night, the ghost returned, even boasting that she knew of his visit to the master. The husband then posed the riddle: "Since you know everything, tell me how many beans are in my hand." Upon hearing the question, the ghost instantly disappeared.