What does Su Dongpo mean when he sees a lump of shit on the Buddha's head?

Su Dongpo's Looking at Buddha and Shit is a famous joke story in ancient times. When Su Dongpo worships Buddha, he finds a lump of shit on the Buddha's head, so he takes out his handkerchief to wipe it. If it can't be wiped off, he wipes it with his hair.

The source of this allusion is the poem "Looking at the Buddha" by Su Shi, a scholar in the Song Dynasty: "Su Dongpo looks at the Buddha with dust on his head. Wipe with a handkerchief. If you can't wipe it off, use your brain. This allusion shows Su Shi's admiration for Buddhism. He thought Buddhism was a noble religion, so he wiped the shit off with his hair to show his reverence for Buddhism.

On one occasion, Su Dongpo and Fo Yin meditated together. After they sat down, they chatted. Su Dongpo asked Fo Yin, "What do you think I look like when I meditate? Fo Yin glanced at Su Dongpo and said, "I think you are like a Buddha. When Su Dongpo saw Fo Yin wearing a yellow frame, he couldn't help saying, "I think you are like shit when you meditate! Fo Yin smiled and said nothing.

Su Dongpo is very happy. He went home and said to Su Xiaomei, "I always talk about Zen with Fo Yin, but I never won. This time I won." As a result, when Su Dongpo told Su Xiaomei what happened, Su Xiaomei said, "Brother, you lost even worse this time!" Why? Fo Yin looks at you like a Buddha, because there is only one Buddha in his heart, so he looks at everything like a Buddha. And brother, what about you?