Idiomatic Allusion to Yellow Ear Sending a Letter

This allusion is from the Book of Jin - Lu Ji biography:

初机有骏犬，名曰黄耳，甚爱之。 Both and detained in the capital, long time no family asked, laugh with the dog said: "my family absolutely no letters, you can take the news of a book not?" The dog shook his tail and made a sound. Machine is a book to the bamboo and tie up the neck, the dog looking for the road south, so to their homes, get the report back to Luo. The first time I saw this, I thought it would be a good idea for me to go back to my old neighborhood.

During the Western Jin Dynasty, there was a famous writer named Lu Ji, who was an official in Luoyang, the capital city of the time, and his hometown was in Huating, Zhejiang Province, which was very far away from each other, and communication was very inconvenient. Lu Ji kept a hunting dog named Huang Er, which was loved by Lu Ji. This hound is extremely spiritual, very smart, can understand human language. Once someone lent it three hundred miles away, it even recognized the road to run home.

Lu Ji is very favorite yellow ears, wherever you go to bring the yellow ears with you. Once, Lu Ji didn't receive a letter from his family for a long time. So he joked with Huang Er and said, "Can you take my letters with you and run back home to deliver the news for me?" Surprisingly, Huang Er actually understood his words, wagging his tail and barking, showing great solicitude and willingness to serve his master.

Lu Ji tried to write a letter, installed in a bamboo tube, set on the neck of the yellow ear. The yellow ear along along the post road, straight to Zhejiang Huating and go. It is hungry to play some wild food to feed, encountered the river, to the transition of people wagging their tails to ask for help, let others take it on the ferry across the river. In this way, this clever hound trekked thousands of mountains and rivers, and finally ran to Lu Ji's hometown.

As soon as he entered the house, he picked up the bamboo tube in his mouth and barked at his family. The family opened the bamboo tube and saw Lu Ji's letter, surprised and happy. When the family finished reading the letter, the yellow ear and rushed to the family called up, Lu Ji's relatives understand, it is asking the family to write a letter back, so they wrote a good letter back into the bamboo tube as it is, still tied to the yellow ear on the neck. The yellow ear jumped and took it along the way back to Luoyang, to the master of the order.

The yellow ear to send a letter, back and forth only spent twenty-five days. If you send someone to deliver the letter, it will take at least 50 days. After that, Lu Ji often asked Huang Er to deliver the letter. Later people used this allusion to describe the delivery of letters.