On Halloween night children would dress up in scary costumes and go house to house. Phrases like "Help the Halloween Party" and "Trick or Treat" were the cries to be heard at each door.
This tradition of wearing costumes also dates back to Celtic times. On the special night when the living and the dead were at their closest the Celtic Druids would dress up in elaborate costumes to disguise themselves as spirits and devils in case they encountered other devils and spirits during the night. By disguising they hoped that they would be able to avoid being carried away at the end of the night. This explains why witches, goblins and ghosts remain the most popular choices for the costumes.