A Cheap Alternative to Mentos Can you believe there's more to say on the Diet Coke and Mentos story? There is. After the last go-round, I sent off a note to Richard Zare at Stanford University. Besides being a world renowned chemist, Zare has a particular fascination with bubbles. He recently showed why the bubbles actually go down the side of the glass when you first pull a pint of Guinness. So I wrote to him, and asked his take on why dropping Mentos in a bottle of Diet Coke caused the bubbly liquid to shoot out. He wrote back from China to say he was sure anything with rough edge dropped into a bubbly soda would do would cause the geyser, including sand or salt. He recently sent this picture and caption to prove his point.