Alliteration in The Raven
Poe creates a strong internal rhyme through the use of alliteration, or repetition of sounds. Throughout the poem, Poe repeats the consonant “s” sounds and deep vowel “or” sounds to create a sonorous effect.
"Silken sad uncertain rustling" is a type of alliteration called susurration. Susurration is soft repetition of the "s" sound. It creates an eerie sense of whispering, hissing, or swishing. But while eerie, it can also have a calming or lulling effect. This line simultaneously shows the narrator's discomfort at this uncanny experience and paints the image of a still, silent room.
Notice Poe's use of subtle alliteration of "S" sounds in these two lines. After sounds in "denser...unseen censer," the reader might expect that to be all. But since Poe is describing a swinging censer containing burning incense, it is pleasantly surprising when the weighty (literary) device seems to swing back at the beginning of the next line with, "Swung by seraphim," two more alliterative "S" sounds.
This is the first example of Poe’s frequent use of alliteration, the repetition of initial sounds, and internal rhyme. Notice how Poe uses internal rhyme throughout the first and third lines of each stanza, and particularly how repetition represents an essential technique and theme in the poem.