I love this deep-dive on the little interjections we use in everyday speech. One example:

Other interjections serve as what some linguists call ‘continuers,’ such as ‘mm-hmm’—signals from the listener that they’re paying attention and the speaker should keep going. The form of the word is well suited to its function: Because ‘mm-hmm’ is made with a closed mouth, it’s clear that the signaler does not intend to speak.