Hey!
I agree with jdstar - when I went to interview at nova, i was just thinking of it as a practice interview. By the end of the day, I was head over heels in love with the school. If you want some in-depth info about interviews, you can pm me and i'll answer it (i'm sorry i'm just not in the mood to type now, and i always write a book), but i'll answer about defending yourself. If you really don't want to talk about your weaknesses you can say it was just personal, but I don't think they necessarily want an explanation. Also, that explanation sort of puts an edge on the conversation/leaves them hanging. I think they really just want to see how you react to the criticism. If you got an interview they already think you're competent. My application had several F's and C's, and I don't have stellar mcats and I had just come from a school that bashed me the whole time during my interview, so I immediately tried to explain the reasons for my grades. My interviewers told me not to worry about it and never touched the subject after that. Just say you tried your hardest, there were extenuating circumstances that made it rough, and if its not acceptable, you'll do anything to improve and will be back next year. One great answer someone in my group gave about poor mcats was that it was him on paper - he knew he could have and should have done better, but in the end, they should judge him on his person not his scores. Hope that helps! And the best of luck!!