It is said that one day Zheng Banqiao was visiting a friend deep in the mountains. As he passed by an ancient temple, he saw a single couplet written on the wall:
"Cun tu (inch of soil) makes si (temple); si with yan (words) makes shi (poem); the poem says: 'The bright moon sends the monk back to the ancient temple.'"
He found this line highly literary. "Cun tu" means a small place, a modest way of referring to the temple. Moreover, combining the characters "cun" and "tu" forms exactly the character "si" (temple). Combining "yan" (言) with "si" (寺) forms precisely the character "shi" (诗, poem). Finally, it circles back to the original word "si" (temple). This fully demonstrates the clever skills of character decomposition, combination, and chain-linking (where the last word of a phrase becomes the first of the next).
He deeply admired it but was troubled because he couldn't think of a matching second line at the moment.
On his way home, Zheng Banqiao happened to see some trees by the roadside leaning haphazardly, with broken branches and damaged trunks. This scene stirred his emotions, and suddenly the second couplet came to him:
"Shuang mu (two trees) make lin (forest); lin with shi (示) makes jin (prohibition); the prohibition says: 'Axes and adzes may enter the mountains and forests only at the proper time.'"