Okay, the nerd part of Lance--which is a pretty big part--is utterly fascinated by all aspects of that answer, but he decides to focus on the latter portion since it's the portion he imagines Carlisle knows more about for obvious reasons. "That's so cool. How does it work?"

And then he stops, suddenly realizing-- "I'm sorry; you don't have to answer if that's too personal." How personal is magic? He has no idea, but the impression of Carlisle he's gotten so far is that he's a little timid and reserved, so he might not want to answer a bunch of questions.