An eleven year old boy setting up a 'Mentos Fountain'. It is a demo of the chemical concepts of physical change and nucleation. Mentos brand mints are dropped into diet soda - the Mentos cause the carbon dioxide in soda to rapidly form into bubbles, resulting in a sudden fountain of soda. The bubbles form so rapidly because the mint breaks surface tension in the soda and because indentations on the candies act as nucleation sites which facilitate bubble formation.