Some ideas...
1. I would have "done my homework" on the program's strengths and weaknesses before my interview.
2. If I did not have any specific questions to ask, I would comment on the program strengths, for example "I've seen that the residents get very competitive fellowships", "there are not too many fellowships in this program, hence a chance to operate more", etc... Those are pretty good examples..
3. I would be very careful, but perhaps I would also comment on the weaknesses if appropriate, to give the impression that "I know what I am after" (which I hope is true for most of us). For example, if I know that the only weakness of the program is spine surgery and I was pretty sure I want to end up doing upper extremity and the program is very good at it, I would stress that I know this weakness but I still consider that the program is great for me. I think this would show to them that I chose to apply to the program carefully, because I know it very well and I think it is perfect for me.