"spills the upper boulders..."See in text(Text of the Poem)
The phrase “spills the upper boulders” displays Frost’s ear for sound play. The words are rich in rhyme, containing both assonance and consonance, not to mention the internal end rhyme in “upper boulders.” Note the repetition of s and p—which finds its consonant pair in b—as well as the repetition of the liquid consonants r and l. These dense sound effects make the language more tangible, strengthening the image of boulders spilling down from the wall.
