Cool. But this site has a funny quote:
This 16-year-old boy from Rabun County, Georgia was the only "authentic" local to play the role of The Banjo Boy in John Boorman's disturbing hit movie of 1972 Deliverance. Billy was hand-picked from his local elementary school largely due to his "look" ( Billy's large head,skinny body, odd-shaped eyes and moronic grin had sadly branded him a poster-child for inbreeding and mental deficiency).
The actual irony is that Billy was neither "retarded" nor even able to "fake" playing the banjo.
I think someone who can't fake playing a banjo might qualify as being a candidate for retard testing. Nonetheless, I always wondered if he could play...and those eyes...