I don't know about everybody else's experiences, but I get the feeling that internship interviews are inconsequential. These sites must know whom they want before you even show up. Every site I have been to has failed to really ask me any hard questions. Matter of fact, all they do is talk about their site. In addition, at many sites I interviewed with faculty whom I would not even be working with. This makes me believe that they determine their picks from the paper applications and interviews are just for show or to make sure you do not have 3 heads, etc.