Its actually really heartbreaking if you know why whistling is there in the song. Otis had done a recording of the song and didn't have a last verse written out yet and so whistled a melody as a placeholder to flush out later. But he died in a plane crash before he could finish the song. So his band leader at the time, Sam Taylor, redid the whistle take that got on the final cut. Its a real gut punch when you know that story.
My great-aunt, Nora Williams, performed in vaudeville during the 1920's and 1930's. She had a minor hit with the song, "Piccolo Pete" and was well known for her whistling skills. Unfortunately, I never met her, but my grandmother (her sister-in-law) and mother adored her.
