just had my uchicago interview, and from my sense of the way this works, and from talking to anthropology grad students, they're mainly looking to confirm that the person behind the application didn't just cobble together a research idea, and that he or she can make intelligent small talk about it.
the first question my POI asked how it was that i had come to conceptualize the project i want to work on the first place, and if i could sketch out an intellectual biography of how my thinking had developed across the years in the various institutions i have been a part of.
the other broad topic that came up was what i was looking for in a grad school, and how uchicago would provide me the best resources to achieve my goals.
it was a pretty relaxed chat, i didn't feel like i was being grilled or anything. while i have no idea how this will eventually turn out, my gut says that, having done some preparation in your head, sorting out ideas and goals etc, you should sit back and let your enthusiasm for research and grad school carry you through. good luck to everyone who has interviews coming up!