This is Just Cool

The Briggs-Rauscher reaction is known as an oscillating chemical reaction. According to Wikipedia: “the freshly prepared colorless solution slowly turns an amber color, suddenly changing to a very dark blue. This slowly fades to colorless and the process repeats, about ten times in the most popular formulation, before ending as a dark blue liquid smelling strongly of iodine.” The reason this occurs is that the first reaction causes certain chemicals to be released in to the liquid, which then, in turn, spark a second reaction, and the process repeats itself until exhausted.
http://listverse.com/science/top-10-amazing-chemical-reactions/