The above are all great suggestions.
I inadvertently asked my Penn interviewers if they were "crazy PETA people". We all laughed pretty hard as I stumbled through the rest of my statement, which consisted of me saying I didn't mean all PETA supporters were crazy but that yeah, they were probably crazy. 🙂
Other than that, I asked about their interests (clinical and research). 30 minutes really isn't long enough!