The fake Shemp was used in place of the real Shemp. Shemp died during the filming of a Three Stooges movie. The footage already shot was used and a stuntman that really didn't look like Shemp at all was used in the dearly departed Shemp's place. They would always try to not show the fake Shemp's face but inadvertently made it really obvious that who you were seeing was not Shemp.