It was a Sunday evening, and I had already gone to Grateful Dead shows at Frost Amphitheater at Stanford on the Saturday and Sunday afternoons, and I was exhausted and wired, but I went to see Stevie Ray Vaughan at the Keystone Palo Alto anyway. I was right at the stage, to the left of SRV's mic in the middle of the stage, and quite close to his wah-wah pedal. After he played two of his fast  instrumentals, he stepped over to that pedal and started doing this crazy stuff with it, and I could not really see him, but I watched his left-handed shadow playing on the back wall. Here's what he did (from a different 1983 performance):

And the moral of Stevie's story is: don't ride helicopters during storms.