Tomorrow night, the 92nd St. Y is presenting Jim Henson’s documentary from 1968. And no—it doesn’t document a day in the life of Kermit and Miss Piggy (but that would sort of be amazing). Before his Muppet days, Henson created a doc called Youth ’68 for NBC’s “Experiment in Television” series, which has yet to be screened since its network premiere. The film juxtaposes interviews with musicians and students with avant-garde stylizations, including appearances by Jefferson Airplane and The Mamas and The Papas.

And now we have our answer to how Henson came up with his brilliant idea of the Muppets: he was a hippie. Maybe that was too obvious.