> It's like saying, "You're kidding!" when you
>believe the person you're talking to is telling
>the truth. The implication isn't that the
>person is a liar, but what he's telling you is
>weird enough so as to be slightly difficult to
>believe.

It's also just part of the natural ebb and flow of human conversation. Nobody (except extreme narcissists or college professors) wants to just talk and have other people listen quietly unless they're specifically telling a long story, in which case they'll usually prewarn the other people by saying something like "That reminds me of the time..."

Words and phrases like "Really?" and "Uh-huh" and "Yeah?" and "Huh" are just placeholder words. It's something you say when you have nothing to say, but you're expected to contribute to the conversation at that point. It allows the person who is really talking a chance to rest for a second, to see who is really listening to him, and to judge the interest in the current topic. It also allows the person listening to encourage or discourage a certain topic of conversation based upon what placeholder words they use or what emphasis they give them, and to prove that they're listening by coming up with something "proper" to say when it's "their turn" to talk.

-- Dave