halloween點解要說trick or treat?

Trick-or-treating, also known as guising, is an activity for children on Halloween in which they proceed from house to house, ....

****** asking for treats such as candy with the question, "Trick or treat?" ******

Trick-or-treating is done in costume and is one of the main traditions of Halloween. It has become socially required if one lives in a neighborhood with children to purchase candy in preparation for trick-or-treaters.

Note. The children bring along the trick-or-treating bags.