[Doc gets thoughtful himself] I'm not sure. I mean, traditionally karaoke is singing along to other music than your own, isn't it? But I don't know if there's any official rules against playing along to the song as well as singing. . .

[Marty nods] Well, while you're thinkin', I'm gonna see if anybody minds me playing something. [he'll ask the bartender, since he's not sure who else to question]