People around the world will celebrate Halloween this Thursday, October 31. Halloween dates to an ancient Celtic tradition in which people believed the dead would return to visit the living. In the United States, many children are busy preparing for Thursday night. They will shout “trick or treat” as they go from home to home in search of candy or other treats. Some children will paint their faces to look like skulls, borrowing from an ancient Aztec tradition falling around the same time. It is called Dia de los Muertos, or the Day of the Dead. The Day of the Dead spread from Mexico and Central America across the U.S. border. It has become big business in the United States. Stores sell Day of the Dead clothing, skulls made of sugar and other products for the celebration.