Reaction of kids when their parents tell them that they have eaten their Halloween candies. Trick-or-treating is a customary celebration for children on Halloween. Children go in costume from house to house, asking for treats such as candy or sometimes money, with the question, "Trick or treat?" The word "trick" refers to a (mostly idle) "threat" to perform mischief on the homeowners or their property if no treat is given. In this custom the child performs some sort of trick, i.e. sings a song or tells a ghost story, to earn their treats.
