Same as Polychorus. Kurt had two of them apparently, and used them on the Unplugged show. However, I don't know what songs he used it on. I don't think he used it one any songs, but Guitar World says that he was arguing with MTV techs over the various qualities of the Echoflangers.
THE FORGOTTEN MARINES OF TARAWA. During late-November 1943 one of the most savage battles in the history of the Marine Corps took place on the tiny island of Betio, located in Tarawa Atoll. The capture of this island took three days and cost the lives of 990 Marines and Navy Corpsmen. In addition to these, another 2,200 were wounded.
Mark Noah squatted down for a look. He is a stocky man of 48, with a light buzz of blond hair and the wind-beaten eyes of a lifelong outdoorsman. Since 2008, he has been traveling to the tiny Pacific atoll of Tarawa to search for the remains of more than 500 Marines who died there in World War II. Sometimes locals dig up their bones and leave them in his storage locker.