I was put in a room with tw0 others and each of us had a topic we wanted to discuss (should abortion be legal, for example, or should marijuana be legal), and we debated amongst ourselves. None of the 3 of us were invited back for a 2nd round interview. They want to see your logic and how you make and respond to arguments.

First round with HR. Second round is a group discussion. Given a topic, there is no right or wrong. I think they are trying to understand your thinking process and how you deal with problems.