My DD was not obsessive like that. She's maybe the opposite extreme-- she gets a kick out of observing OTHER people interacting with her.
Her "tell" was that she was masterful at manipulating other human beings into completely natural, 'resting state' interactions with her-- within minutes, and without them even realizing it. You could always tell when they realized that they were talking to her the way that they would a close friend that they'd known for years... and this was when she was 3-4yo. She wasn't as 'smooth' then. NOW, most people never notice it. They often remember her as "Oh yeah, that pleasant girl who was so interested in {my passion}."
I think it's her way of extracting the expertise from anyone that she meets-- on ANY topic whatsoever. She figures that everyone has something to teach her, or at least is more interesting when they are talking about what they love, anyway. The only people who truly notice it now are the people that are specialists in human behavior somehow, or those that she allows to see it. Everyone else seems to assume that she is a committed future protege, even if her actual level of interest in the subject is more like "tepid at best." Her "tepid" is more like most people's "avid."
She's voracious and intense, though-- that much is definitely classic PG. I'm not sure that I'd call anything else that she does "obsessive" unless it might be reading. She's a biblioholic of the first order.
