Anyone who knows anything about musicals knows they require endless rehearsals in order to be staged successfully. Fred Astaire and Ginger Rogers didn't just jump up and glide around a sound stage as the cameras rolled; they had to practice each step of those seemingly effortless dance routines over and over, for weeks at a time.

There is even a subgenre of movie musicals about the sweat and glory of putting on a musical, with the choreographer usually looking impatient and irritated — or nearly dying of a stress-induced heart attack, as did Roy Schneider's character in Bob Fosse's "All That Jazz" (1979).

Not always so obvious is the intricate choreography required for action scenes, from the apparently chaotic bar-room brawls in classic Westerns to the death-defying stunts of Jackie Chan in his Hong Kong martial-arts extravaganzas.