One was a large piece of yarn stretched from ceiling to floor, and then across the floor for about 15 feet, and then back up. Dozens of people walked around it, and no one stepped over it. It was the flimsiest effective barrier I’ve ever seen, and the artist described it as the simplest painting ever: a single line that was both frame and canvas, stretching from one beginning point to an ending one. Also cool: a long white board with a stretched out row of pennies dated from 1967 to 2003; every year until he dies, the artist is going to add one more to the shelf.