Why does this work?

  Carbon Dioxide is pumped into containers of soda to make it "fizz". Surface tension holds the gas within the water molecules comprising the beverage. Shaking a can of soda breaks the surface tension, freeing the gas from the water molecules. Open the can, and the gas and soda are released rapidly.

  Mentos mints are made with gum arabic, a resin which makes the breakdown of surface tension easier. The Mentos also disolve rapidly when they enter the soda, creating many tiny pits on the surface. When objects are dropped into a container of soda, bubbles will form on the surface of the object. The tiny pits provide more surface area on which bubbles can form. And, the heavy weight of the Mentos candy causes the candy to sink quickly to the bottom of the container. The combination of these effects causes the contents of the bottle to be pushed out rapidly.