A man from the state of Wei claimed he could carve a figure of a rhesus monkey on the tip of a sour jujube thorn.
The King of Yan believed him and granted him a generous salary.
A blacksmith heard of this and went to see the king. He said, "I make carving knives, and I know all delicate ornaments are carved with such tools. Logically, the object to be carved must be larger than the knife's tip. The tip of a thorn is far smaller than that of any knife. How could one carve on it? If Your Majesty has doubts, simply ask him to show his carving knife. Then you will know the truth."
Upon hearing the king's request to see his knife, the man from Wei knew his deceitful trick had been exposed. He gathered his belongings and fled in secret.