Just enjoy yourself. Honestly, unless you say you hate patients or that it's your "safety school," you can't really do anything that's going to screw up your chances on a tour. Every school's student body will tell you that they are happy--in fact, if you're actually at a school where they don't, that would be a red flag, cuz it's gotta be pretty bad for them to not at least fake it for the people touring. Ask instead about the curriculum and how much time is spent in class; if you're a self-study kind of person, you might not want to be at a school that's in class 9-4 every day, but on the other hand, if you're an audio learner who likes the structure of lecture, that might be a plus for you.