It's a chemical reaction. Menthol is contained in peppermint candies, while carbon dioxide and carbonic acid are contained in colas. When the mints enter the cola, the menthol reacts with the carbonic acid to form a substance called "mentholic acid". Menthol is an unstable compound that breaks down into water and carbon dioxide and releases large amounts of gas. Therefore, the reaction between menthol and Coke is a chemical reaction that produces a large amount of gas and foam, causing the Coke bottle to explode.