Before the invention of paper by Cai Lun during the Eastern Han Dynasty, the earliest books were handwritten on bamboo slips. With thousands of Chinese characters, books relied on repeated copying to circulate, which inevitably led to a common flaw: characters with similar shapes were frequently miscopied.
During the Spring and Autumn period, Confucius' disciple Zixia was preparing to go to the state of Jin. Passing through the capital of Wei, he once lodged at an official's home. One evening, while strolling in the courtyard, he saw the official holding a book and reading aloud in a loud voice.
"The Jin army had three pigs crossing the Yellow River." Zixia, well-versed in Jin history, found this strange and thought, "How could there be pigs in the Jin army? And how could pigs cross the Yellow River?"
Zixia stepped forward and asked the official, "May I borrow that document to take a look?" The official handed him the scroll.
Zi Xia took the book and carefully read the passage in context, suddenly realizing it described a battle between the states of Jin and Qin. He immediately declared, "The original text must have read, 'The Jin army crossed the Yellow River in the year Jihai.' The characters for 'three' and 'ji,' as well as 'pig' and 'hai,' look similar, so a copyist mistakenly wrote them wrong."
The official, though skeptical, could not immediately verify Zixia's claim. Later, while on a mission to the state of Jin, he made a point to consult the Jin court historian—and discovered that Zixia's explanation was entirely accurate.
In the Eastern Jin Dynasty, Ge Hong's work *Baopuzi* recorded a folk proverb about transcription errors in ancient texts: "After three copyings, 'fish' becomes 'Lu,' and 'void' becomes 'tiger.'" This means that after repeated copying, the character for "fish" was mistaken for the character "Lu," and the character for "void" was mistaken for "tiger." Later, people used the phrase "Lu fish and pig" to describe textual errors made during the copying and printing of books.
Source: *Lüshi Chunqiu*, Chapter "Examining Traditions"
Meaning of the Idiom: Later, the Chinese idiom "鲁鱼亥豕" came to describe how textual errors are made during the copying and printing of books.