the guy under the curtain IS mark, he did that on several nights on the tour, a couple of em he wud follow on bass, this was on the Loserkids tour, the night i saw em mark did it :P
If you look at the subtle differences between the views, you'll notice they're from 2 different shows. That's why Mark can be playing bass and peeking under the curtain at the same time, haha. (i.e. he has shorts on in the side view and a red atticus shirt while he has the white one on in the front and pants)
no it is mark, this was shot two different nights. you can see it. mark's playing on stage at different times and there is a spot light on him while when you see tom alone, it's only one spotlight. i think cheetah filmed it on two different nights.