“Surely my mustache will comfort you.” says Salvador Dalí, lost in the sweet monomaniacal reverie that is John Collins’s Marx Brothers on Horseback Salad, a greatly imagined play about Dalí’s lost screenplay for the Marx Brothers. Eerie and funny, it’s part of The American Living Room, the Tiny Mythic Theatre Company’s highly casual summer cabaret, which features three new shows by three different directors every weekend. With “Ode to Billy Joe” as Muzak, a harp strung with barbed wire scooting around the stage, and dismembered arms flying to and fro, Horseback Salad is dreamily intuitive art-slapstick — Collins’s theatrical vision undeniable.