In late 1973, Zappa brought Napoleon Murphy Brock into his group and almost immediately the entire vibe of Zappa’s music changed. Between his sax playing, improvised comedy bits and singing, he’s all over Roxy. But this group was also very tight: just listen to them tackling the tricky figures on “Don’t You Ever Wash That Thing,” which climaxes with a tasty Duke solo and percussion duet. Zappa, meanwhile, gets to stretch out with a solo of his own on “Son of Orange County.” And everyone, even the audience, gets to party with the dance contest on “Be-Bop Tango.”