My initial interview was a "group interview" where they brought a bunch of people in together. I'm pretty sure that the point of the interview was just to see how you interact with others in the various activities. They also told us all to give a short (~3 minute) presentation on "anything you want". They really do mean "anything". It could be making a Peanut Butter sandwich. It could be your hobby. It could be an interesting medical technology that is just coming out. It's less about the content and more about how you carry yourself.