The Wytches' furious, hair-flinging psych-rock isn't the stuff of back-porch acoustic sessions: Both live and on the English band's singles, the energy is so intense, it can barely be contained. But when NPR Music arranged a Wytches session during SXSW — held in the charming backyard setting of Friends & Neighbors in east Austin — singer-guitarist Kristian Bell stood in for the whole band, with just his voice and an acoustic guitar.