1- The answer to question 1 is: " it creates the impression that the world of nature is alive with interactions." The grass does not dance , in fact the wind makes it move. In the poem, the grass dances to the tunes the wind plays. The interaction is here. The wind does not play music ; it makes some sound while the air moves, though. This dance between the grass and the wind is what creates the impression the world of nature is alive.
2- The answer to question 2 is: " It helps readers to better imagine the motionlessness of the moon in contrast to the movement of the dune grass." " But the moon above is a statue." The use of "but" shows the contrast between the movement of the grass and the motionlessness of the moon. Besides, a statue is a motionless object and silent.