Please Advise
When someone is telling a story that you've heard already, but the person forgot that they told you, but you know that other people in the group haven't heard the story so you can't say, "Yeah, you told me about that," but the person is looking at you for a reaction, do you pretend you are hearing it for the first time, which could backfire later if the person remembers that they told you and wonders why you forgot about it so fast, or do you just nod sagely, which might make the person think you don't give a crap about their story?