3000 years ago, Celts celebrated Samhain when they believed spirits and dark forces were active. Now on Halloween, children dress up in costumes and go door-to-door saying "trick or treat" to collect candy and sweets. People carve faces into pumpkins and use them as decorations called jack-o-lanterns. Special Halloween foods are made to look scary but are tasty, and there are spooky songs to sing and dance to celebrate the fun holiday.