True story: I answered an advert for a crowd scene being filmed at the Lincoln Memorial, for Milos Forman's film of the musical 'Hair'. They filmed a bunch of folk (couple of thousand of us showed up), and if the final film had let the crowd scene run under the end- credits for juuuust a few seconds more, I would have made my Hollyweird debut.
C'est la vie.
At least I got to see the filming of another scene (cut from the release), and was entertained by comedian Robert Klein before the filming; after the filming, there was a performance by this young, red-haired singer I'd not heard of before, named Bonnie Raitt.