The lines in the poem that best demonstrate the use of assonance are: "The grass divides as with a comb, / a spotted shaft is seen." In these lines, the repetition of the long "a" sound in the words "grass," "divides," "comb," "spotted," and "shaft" creates a pleasing and rhythmic effect. This repetition of sounds, known as assonance, is a literary technique that is often used in poetry to create a specific effect or mood