As the album title indicates, Halloween 73 was recorded on Oct. 31, 1973, over the course of two shows at the Auditorium Theatre in Chicago. With the exception of a handful of songs, the two 19-cut sets are different, so fans who managed to wrangle tickets to both shows got a whole bunch of glimpses into the mind of the much-beloved weirdo genius. The first show begins with Frank introducing the band members (George Duke, Ruth Underwood, Chester Thompson, Napoleon Murphy Brock, Ralph Humphrey, Tom Fowler and Bruce Fowler) before launching into the new at the time "Pygmy Twylyte," "The Idiot Bastard Son" and "Cheepnis," which Zappa instructs the band to play not as fast as usual so that the audience can understand the words. Famed for playing medleys, or "assemblies" as Zappa calls them, the band strings seven songs together for the mid-section of the show: "The Eric Dolphy Memorial Barbecue," "Kung Fu," "Penguin in Bondage" (dedicated to the "pervert's special holiday" as Zappa dubs Halloween), "T'Mershi Duween," "The Dog Breath Variations," "Uncle Meat" and "RDNZL" (pronounced "Redonzel.") Zappa visits the land of pygmy ponies and dental floss bushes with a take on "Montana" and the band really stretches out for a 20-minute groove on "Dupree's Paradise" before wrapping things up with "Dickie's Such an A**hole."

The second show presented on Halloween 73 repeats performances of "Cheepnis," Dickie's Such…," "RDNZL," "Penguin in Bondage," "T'Mershi Duween" and a few others but also features favorites "I'm the Slime," "Cosmik Debris" and an 11-minute take on "Inca Roads." A 16-minute medley of older songs "Son of Mr. Green Genes," "King Kong" and "Chunga's Revenge" closes the set. Zappa fans will love what appears as bonus material; a dozen songs committed to tape during rehearsal. Of course with Zappa's well-known perfectionism fully in place, the rehearsals are mostly fully-formed songs (although there is some chatter and instruction from Frank) and the groove the band hits on the percussion-heavy "T'Mershi Duween" is exemplary, as is the funky "Magic Fingers." Also in the rehearsal set are "Inca Roads," "Big Swifty," "Uncle Meat," "Dog Breath Variations," "Cosmik Debris" and other goodies.