Why do pop rocks make coke fizz?

When Pop Rocks are dropped into Coca-Cola, the candy's compressed carbon dioxide gas bubbles escape rapidly due to the lower pressure in the liquid. This reaction causes the characteristic fizzing and bubbling effect. The bubbles attach themselves to nucleation sites on the surface of the candy and then quickly rise to the surface, carrying bits of flavour crystals with them. This creates a "pop" sensation on the tongue and a pleasurable drinking experience.