I seem to recall a Halloween horror movie starting out this way.
A group of small kids come up to the door in cute costumes and say, "Trick or Treat!" They walk off together with the candy. As the owner is about to close the door, she notices a teen, hanging in the back behind the kids. He's all dressed in black, wearing a white ghoul face mask. "Oh! I almost didn't see you. I didn't think there were any teens living so far out this way anymore." She peers around, "You didn't come with any friends? Well, that's okay. That means more for you then! Here you go!" She hands him some candy. He never talks. He looks down strangely at the candy given to him, then wanders off as the owner closes the door. It is then we close in on the ghoul's face and learn the ghoul face mask is not a mask. That is actually his face.
Remember, All Hallows' Eve, or Halloween is when the separation between the worlds of the living and the dead is thinnest. This "thin veil" is thought to allow spirits and ancestors to more easily cross over to the human world.