D.A. Pennebaker's cinéma vérité documentary Dont Look Back [sic] followed Bob Dylan on his celebrated 1965 tour through England, letting viewers see what happened along the way -- the good, the bad and everything between. Today, it's considered both a classic documentary and a pop-cultural artifact, something Dylan fans can't afford to miss.
The same can't be said for Eat the Document, Pennebaker's follow-up documentary that captured Dylan's return to the UK in 1966. The premise had promise. Bob Dylan had just gone electric and boos followed him wherever he went. In Manchester, they famously called him "Judas." That could have made for an intriguing film. But, according to Dylan's most recent biographer Daniel Mark Epstein, the singer-songwriter was personally unraveling. He had toured to the point of exhaustion, and taken far too many amphetamines. During one moment filmed by Pennebaker, Dylan shared an incoherent taxi ride with John Lennon. Their rambling conversation touched on Johnny Cash, The Mamas & the Papas, Dylan's homesickness, and how the Thames River supposedly saved Britain from Hitler. And, once we get 20 minutes into the footage, we find Dylan slumped forward in the backseat, seemingly staving off nausea.
Dylan personally edited the film and gave ABC television the option to air it. The network declined, saying it wouldn't be comprehensible to a mainstream audience. Because the film was never released, it has been passed around in various bootlegged versions. You can watch a 52-minute version on DylanTube.
As a quick footnote, it's worth mentioning that, according to Epstein's biography, Lennon later told Rolling Stone magazine that he and Dylan were doing "junk" (aka heroin) that day, and that Lennon thought Dylan was close to OD'ing. It's all discussed in The Ballad of Bob Dylan: A Portrait.