This is a fun number choreographed by the great Hermes Pan. Russ Tamblyn is a stranger who happens to be wearing the same outfit as the other male dancers and joins in, and it's really interesting choreography.
I've rarely thought about Hermes Pan, but now I'm going to start looking for his work.
He had a remarkable resemblance to Fred Astaire. From behind he was mistaken for Astaire on the set. I know it is written that Astaire invented his dance numbers with Pan and then brought in Ginger Rogers but she was in only 2 other films during the peak of their fame.
