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Roosevelt Grier, whose character plays the cello for a jazz combo, at one point plucks the instrument like a bass with one hand, and holds the note with vibrato on the other: like he knows what he's doing. A few years later, in The Glove (1979) he displays a genuine talent for playing guitar.
Charlton Heston reportedly took the lead role so that MGM would allow him to use footage from Ben-Hur (1959) for his directorial debut, Antony and Cleopatra (1972).
Charlton Heston tells in his biography that director John Guillermin was a very effective filmmaker but also liked to humiliate actors from time to time.