It's interesting that his new acquaintance seems mildly excited about research -- some people do, it's a type, but still interesting to meet someone of that type. It may be that they're useful acquaintances in the future, or it may be that it's a good idea to keep an eye on them, particularly if their curiosity seems to lack normal limits and they'll do anything to satisfy it.

"Physical research...?" That's an invitation to elaborate on that idea, accompanied by a tilt of L's head and a slight narrowing of his wide eyes.