The Grateful Dead, god love 'em, were not above telling a bald-faced lie or two on-stage. And they open this show with an important one, pretending to the audience that they have to do an impromptu acoustic show because "Bill is an airplane somewhere over Omaha" at the moment.
In reality, he was sitting backstage. This is one of the first times the Dead went "full acoustic;" they would pretend it was accidental until February 1970. After the experiment, Bill rejoins and you get a great Dark Star.
