so both guitars are playing the same riff, but one of them's playing it without the last note, so it's in 13/8 instead of 7/4, right? and every time they play the riff the second guitar lags behind by an extra note, and they get more and more out of sync until eventually they're exactly one bar apart and they start playing at the same time again. it's some crazy shit bro, you gotta hear it.