The "Mentos effect" occurs when a Mentos mint, the cult candy associated with dorky 1990s commercials, is dropped into cola, especially diet cola, and usually Diet Coke (although some claim that Diet Pepsi works just as well). The cola immediately fizzes over with geyser-like force, and clips of the reaction, including some choreographed Mentos effect "performance art" have cropped all over sites like YouTube.
But what causes it?
Brian P. Coppola, an Arthur F. Thurnau chemistry professor at the University of Michigan answers this question in this Ann Arbor News article "Frothy mystery: mentos plus diet cola equals drama" by Tracy Davis.
Submitted by Tracy Davis, Ann Arbor, Mich.