What do boys want to express when they say that the spring mountains are like black grass and the grass is like smoke?

Express differences.

1. Boys say that the spring mountains are like black grass and smoke, which means they want to express separation. The spring mountains are like black grass and smoke, which comes from the poem "Four of Four Sensations of the Past" written by Huang Jingren, a poet of the Qing Dynasty, "From now on, the sound will be forgotten." Everyone is quiet, the spring mountains are like black grass and smoke."

2. "Four of Four Poems on the Past" tells the poet Huang Jingren's longing for his separated lovers, and also expresses the pain of separation between lovers.