The poetic elements you're referring to are:
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Alliteration: This refers to the repetition of the same sound at the beginning of two or more words in close proximity. For example, "She sells sea shells by the sea shore." The 's' sound is repeated at the beginning of each relevant word.
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Consonance: This describes the repetition of the same consonant sound in various positions within several words in a line or section of text. An example is the phrase "The lumpy, bumpy road," where the 'm' and 'p' sounds recur within different words.
These elements contribute to the rhythm, mood, and musicality of poetry and prose.