Night fell on the Austin City Limits Music Festival at Zilker Park this past Sunday under a full moon and over a sea of mud. (It wasn't strictly mud, but more on that in a bit.) Many in the crowd, especially those in the proximity of the Dell stage, responded the only logical way possible — by dancing, or something close to it. Since the squishy, slippery ground made it a little difficult to move your feet — people weren't so much walking through the grounds at this point as gingerly creeping — Spearhead stepped in to pick up the...