Why does the poet's pen walk on his knees when he writes about his mother?

Be grateful for your mother's love. According to the query of China Poetry Network, the mother in the poem became a kind poem, and she became a pen in her hand. Between these two staggered comparisons, there is an anthropomorphic form of grace that kneels and suckles, "kneeling and walking", thanking her for her deep love. Memories of New Year's Eve by Sang Hengchang: Whenever I write about my mother, my pen always walks on my knee. If my mother were a fish, she would peel off all the scales with blood and make clothes for her children. My mother spun an umbilical cord by the light of lanterns, and I turned it into a Wan Li. There are surging rivers everywhere. Tonight, my mother will wait for me at the intersection of the end of the year and the beginning of the year, and uproot my son again.