A tale of movement, the author is unknown.

I was in a bar in San Francisco during a vacation. They had this go-go girl on stage dancing.

I was the only customer in the bar, so the bartender talked to me. He told me that he employed twin dancers ,named Shelly and Jan, who were working their way through college. He also said that they alternated. One day Shelly would be on the stage and Jan would be studying. And the next day Jan would be on the stage and Shelly would be studying.

I asked him which girl was on the stage that day. He turned around, looked, and said, “It must be Shelly ’cause Jan don’t shake like that.”