It is often said, when analyzing poems, that alliteration is the effect created by using successive words beginning with the same first letter, which is true, but which does not actually identify why the poet has chosen to use this technique or what effect is derived from it. A clue when we are trying to understand this is to identify which letters are being used alliteratively, and what difference this makes. For example, alliteration on the letter "s" creates a sibilant, snakelike quality and suggests whispering; in the same way, the letters which alliterate here give different sound effects and suggest different images to the reader.

The repeated "n" sound, for example, is staccato in a way that seems to imitate the nodding the speaker is doing as he tries to stay away, "nearly napping": it seems to evoke the feeling of one's head drooping forward and then being jolted to alertness again. The "n" sound is also contrasted directly, through the use of rhyme, with the "t" in "tapping." "T" is a very clear and sharp sound which seems to evoke the feeling of being pulled back sharply to alertness.

Alliteration is the repetition of initial consonant sounds in words that are close to each other in the text. Here the words "nodded, nearly napping" all begin with the /n/ sound, and the three words occur in sequence. The alliteration ties the three words together by their first sound. The /n/ sound is a soft, smooth sound; it is a nasal consonant. To make the /n/ sound, air is stopped from coming out of the mouth because of where the tongue is placed and is forced to come out of the nose. Interestingly, this sound is the same sound that someone might make inadvertently while sleeping--a deep breathing sound that is not quite a snore. So using the repeated /n/ sound to describe someone who is about to fall asleep helps the reader experience that state simply through the sounds of the words. In addition, the fact that the three words have identical rhythm--a stressed syllable followed by an unstressed syllable--reinforces the effect. One can almost feel the sensation of the man's head starting to droop and the man catching it with each new stressed /n/ syllable. The use of alliteration and rhythm in this way helps the reader enter into the mood and action of the poem.