I am writing a novel and am constantly trying to figure out how to describe the action when someone gives a sort of small cough or a quick "huh" in agreement. I suppose it would be the non-word equivalent of "I'll say" or "You think?" To be specific, I'll use it in a dialogue.
"He must really hate Ian, then."
Clarissa [insert word here]. "Yes."
It's usually used when the speaker is trying to convey that the subject is much more serious than their conversation partner is taking it.