Road:
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A quick, positive "uh huh" can simply mean "yes," "I agree," or "I understand". It can also be used informally to show you are listening and to imply that a favor was no big deal.
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Saying "uh huh" in a flat, drawn-out, or exaggerated tone can be a way of expressing disbelief, annoyance, or that you disagree with what is being said. The sarcastic use implies the opposite of the literal meaning of the word.
DeKay

