Your prepared questions are great, but your spontaneous questions will be better. Stay engaged with what the interviewer is saying. Some of it will resonate with your research- mention how. Some of it will just plain make you curious. Don't be shy.
If you don’t think it’s appropriate to interrupt, go back to a point in the conversation when there is a break.
If the discussion shifts from a back and forth to a real conversation and exchange of ideas, the interview is bound to be a success.
Curious, intelligent, easy to talk to: three impressions you would like to leave with an interviewer. The best way to achieve this is to ask the questions your interview genuinely inspires.