During the ancient times, there was a Prime Minister surnamed Zhang who loved calligraphy, especially cursive script. His cursive writing was so irregular that even experts struggled to read it. When people offered suggestions, he not only refused to accept them humbly but also blamed others for their lack of skill.
One day, with nothing pressing to do, he picked up his brush to practice calligraphy in his study. Struck by a sudden inspiration, he dashed off a fine phrase in cursive script. The strokes flew across the paper like dragons and snakes, characters linking to characters in a powerful, flowing rhythm. After finishing, he hung the piece on the wall, stepped back, and admired it from every angle, feeling thoroughly pleased with his work.
At that moment, his nephew entered the study and asked, "Uncle, did you write this?" "Fool, if I didn't write it, who could produce such fine calligraphy!" he said cheerfully. "Aren't you also practicing calligraphy? You can copy it now."
The nephew picked up the brush, spread out the paper, and began copying stroke by stroke. As he wrote, he found one character too scribbled to recognize, so he asked:
"What character is this?" the nephew asked. "How can you not recognize it? Look more carefully," the uncle replied. After staring for a while, the nephew still couldn't make it out and said, "I still don't know." Grand Councilor Zhang walked over to the character, examined it for a long time, and finally admitted he couldn't identify it either. He then scolded his nephew, "Why didn't you ask earlier? Now even I can't tell what character this is." Later, the idiom "Dragon and Serpent in Flight" came to describe calligraphy with vigorous, lively brushwork.
Source: Shi Huihong (Song Dynasty), *Cold Studio Night Talks*
Meaning of the Idiom: Later, the Chinese idiom "龙蛇飞动" came to describe calligraphy with vigorous, lively brushwork.