A) awesome.
2) proof that music—specifically, in this case, rock, but all genres, really—is a collaboration between artist and audience and that it does not belong just to the performer, not by a long stretch.
Just check out what happens when Matt Nathanson jokingly starts to play an AC/DC song and soon has to just hold on for dear life as it instantly spirals out of his control.
The bemused looks that pass between the guest and drummer at the very beginning, the look of utter astonishment on Nathanson's face when it takes off, the moment when he points at the guitarist questioning, and the guitarist nods, letting Nathanson know not to worry, that he's got the solo covered...amazing.
As a wise man once said,
Rock is art and a million other things as well—it's an indescribable form of communication and entertainment combined, and it's a two-way thing with very complex but real feedback processes as well. I don't think there's anything to match it.(That same man also wrote, but did not sing, "it's the singer, not the song, that makes the music move along." He was right in both cases.)
