As early as the Spring and Autumn period, people already knew that softshell turtle was a delicious delicacy. Turtles thrived in the waters and marshes of Chu, where lakes and rivers abounded, making them plentiful. In contrast, Zheng was located in a dry, mountainous region, so turtles became a rare and prized commodity there.
Once, someone from the state of Chu sent several large softshell turtles to Duke Ling of Zheng. When Minister Zigong heard the news, he rushed over excitedly to ask when the duke would host a turtle feast. On the way, he happened to run into Gongzi Guisheng, the duke's son. Unable to contain his delight, Zigong wiggled his index finger at Guisheng and said, "Look, whenever my finger twitches like this, I'm sure to taste something delicious."
As they talked, the two entered Duke Ling of Zheng's courtyard. At the kitchen door, the chef was busy slaughtering a turtle. Zigong and Guisheng exchanged glances and burst out laughing. Duke Ling of Zheng, watching the chef work, heard their laughter and asked, "What are you laughing at?"
Prince Guisheng stopped laughing and told his father, "Zigong just said that whenever his index finger twitches, he knows a delicacy is coming—and sure enough, we're about to eat turtle." Duke Ling of Zheng was irritated upon hearing this. Zigong often spoke rudely and had embarrassed the duke many times before. "This time, I'll make him uncomfortable too," Duke Ling thought to himself.
The feast began with a massive bronze tripod filled with steaming turtle soup, its rich aroma filling the air. Following Duke Ling of Zheng's orders, attendants moved the tripod before him as his invited ministers took their seats, each with an empty plate set on their low table.
Duke Ling of Zheng said to his ministers, "Today I invite you all to taste the delicious softshell turtle, but unfortunately there is too little for each person to have only one piece. Let us begin."
The officials approached the great tripod one by one, each receiving a piece of turtle meat and a ladle of broth from the attendants. Zigong also stepped forward, craning his neck to peer into the cauldron, hoping for a larger portion. But the attendant seemed not to see him, offering nothing. When the turtle was all gone without a share for him, Zigong grew furious. He flung his empty plate aside, thrust his index finger into the broth, dipped it, tasted it, then turned and strode out.
Duke Ling of Zheng, enraged by Zigong's actions, gritted his teeth and said, "I will kill this man!"
Before Zheng Linggong could devise a pretext to execute him, Zigong struck first, inciting Prince Guisheng to assassinate the ruler.
The idiom "Finger Twitching" refers to an omen of delicious food to come.
Source: *Zuo Zhuan*, Chapter "Duke Xuan, Year 4"
Meaning of the Idiom: Later, the Chinese idiom "食指大动" came to describe an omen of delicious food to come.