The words "shutter" and "flutter" are examples of rhyme scheme, as they share a similar ending sound. However, they can also be seen as examples of internal rhyme if they occur within the same line of poetry.
If they occur at the beginning of consecutive lines, they are more likely illustrating alliteration due to their initial consonant sounds being the same.
So, the most precise answer would depend on the context in which the words are used. If they are within the same line, the answer would be internal rhyme; if they are at the start of consecutive lines or within a pattern, then you could lean towards alliteration.
Please provide the context or the full line to clarify further!