1974 Giro d'Italia: Fans of the Giro d'Italia love it for its unpredictability, its difficulty, its confusion. Last week we looked at the documentary about the 1973 race, “Stars and Watercarriers,” and in 1974 many of those same stars returned for a rematch. The results are shown in “The Greatest Show on Earth,” produced by German filmmakers, with a very different viewpoint.