Cascarones are empty eggshells that are filled with pica-pica paper confetti and then covered up with another piece of papel china (tissue paper) and finally painted in colorful ways; like everything else in Guatemala. The final painted eggshells are reserved for the Carnaval as it is known carnival in Spanish which is the ‘Sad Tuesday’ before Ash Wednesday; why ‘Sad Tuesday’?, well carnival means “farewell to meat”, you can only be sad if you are going to keep a vegetarian lent.
Actually for an in-depth and more serious explanation, I believe it is better to read Manolo’s comment and the other comments in the entry Guatemalan Carnival Cascarones. The only thing I would add to the awesome explanations is the fact that you can also purchase cascarones in the tienda (your local convenience store) for about 25 centavos each. Twenty-five centavos is the equivalent of 3 cents from the U.S. Dollar. Centavos are the subdivision of the Quetzal, Guatemala’s currency, and there are 100 centavos in 1 Quetzal (about 12 cents).
Okay, I am taking orders, how many cascarones will you need to break into the head of the cascarrabias (grumpies)?