What metaphor does Cao Zhi use for himself?

Cao Zhi compares himself to beans. According to Shi Shuo Xin Yu, Cao Zhi's brother Cao Pi wanted to persecute Cao Zhi after he proclaimed himself emperor, so he ordered Cao Zhi to write a poem in just seven steps. As a result, Cao Zhi sang this seven-step poem. The poet used the metaphor of fried beans to accuse Cao Pi of cruel persecution of himself and other brothers. Beans and beanstalks are born from the same root, just like brothers. The bean stalks are burning in the pot and boiling the beans until they cry. The metaphor of elder brother forcing younger brother is very apt and touching.