Really?

Have you ever had a conversation with someone, and at the end they say "Really?"? Now have you ever thought about why people say that? Are they automatically assuming we're lying and need another confirmation that the aforementioned conversation was honest or valid? Like we're just making stuff up.

"Blah. Blah. Blah. Blah."

"Really?"

"Nope. I just lied to your face."

Or are they just feigning interest and using the word "really" as some kind of half hearted response to whatever it was that we were saying? Kind of showing they were listening while giving the appearance that they actually took in and thought about the previous five minutes of dissertation we just spewed out. Either way its kind of useless don't you think. The word of the day is "bargain".