"What if you received a letter from hell?" is the opening line in a popular video, "A Letter from Hell," about a usually off-limits topic. Tonight, little children across the country will traipse from door to door costumed as various denizens of the underworld: goblins, devils, zombies, ghosts and demons. The holiday's origins are borderline theological in that it acknowledges the existence of "hallows," an old English word for dead spirits. And a dead spirit is who wrote the "letter." Click to view the video: "Dear Zack," says a voice-over from "Josh," a teenager. "I died today. It's a lot...