My dad also plays a little banjo and guitar, my mom plays the mandolin.
You can't force something like that. But we have encouraged our audience, because we avoid the confrontation of regular rock concerts: us up here, you down there. Instead, we're looking for interaction.
Each of our 900 shows so far was different - maybe that's what makes the fans come back to our gigs time and again. And that they're always part of the show. Phish concerts are a communal experience.
