Interpretation: The metaphor is that one is not as good as the other, and it gets worse and worse.

Allusion: This idiom is quoted in Qing Zhai Hao's "Popular Edition" quoting Song Anonymous's "The Relics of the Holy Song": "Tao Gu served Wu Yue as an envoy, and was loyal to King Yi for banquets. With its addiction to crabs, he listed more than ten species from < unk > < unk > (a sea crab) to < unk > < unk > (a small crab). Gu Xiao said: 'It really is said that a crab is not as good as a crab.'"

In the Song Dynasty, there was a man named Tao Gu, named Xiushi. This man had a hobby — he loved to eat crabs. Once Tao Gu was sent by the imperial court to send an envoy to Wu Yue (one of the ten kingdoms in the five dynasties, in what is now Zhejiang, southwest Jiangsu, and northeastern Fujian), and King Zhongyi of Wu Yue gave a banquet to entertain him. Because Tao Gu liked to eat crabs, King Zhongyi ordered people to put out all kinds of crabs at the banquet, from large to small, a total of more than a dozen kinds. Seeing this, Tao Gu smiled and said, "This is really a crab that is inferior to a crab!" "A crab is better than a crab" The original meaning is that one crab is inferior to another. Later, people quoted it as an idiom, which is often used to describe that one being inferior to the other, and it is getting worse and worse.