My father thought it was true!
It's not that he's naive or uninformed or anything, but he watches so many startling documentaries on the History Channel, etc, and is always amazed by how "truth is stranger than fiction" that when he randomly tuned into Zelig about ten minutes into the film, the faked archival footage was so convincingly shot and processed that he was lured into the outrageousness of it little by little, laughing his head off at some of the more outlandish remarks. Immediately afterwards he started gushing to me about this 'amazing' thing he'd just watched on the Arena channel, which usually doesn't show "movies" then paused a moment after noting my expression and said "It was bull***t, wasn't it?" When I nodded yes, he then said "I thought it was going too far when he flew that plane upside down!!"
I haven't seen that film since, but I know that when I do, again, I'll never be able to watch each scene the same way again.
He was doubly sheepish about it because he thought he should have learned his lesson when I sent him a copy of Peter Jackson's "Forgotten Silver" some years back (without giving him a word of explanation about it) and he'd bought into that one too.
I think in the case of Zelig, the truly stoopid would never believe it to be true as they lack the imaginative capacity. As George Orwell said - "there are some things so absurd that only an intellectual can believe them"