Take a clue from the Internet. A short while back, a trick involving a still photo of scenery and instructions to search for a hidden ghost made its way from computer to computer. After about thirty seconds, the photo would change to a ghoulish face, and the computer speakers would emit a blood-curdling scream, scaring the trick’s victims half to death.
You can do this with your front window, if you have the right materials. Fill the inside of the window with a dark background (a few flattened garbage bags, taped together, should do the trick), and keep the lights off. Have an accomplice dress up in a scary costume, with an ugly mask, and crouch beneath the window, inside the house.
Tell trick-or-treaters (with a serious air) that you think your house is haunted, and that you’re sure only children can see the ghost – you want them to confirm it for you. While they’re looking in the window, encourage them to keep staring, and after a few seconds, have your accomplice jump up and roar or scream. If the accomplice points a flashlight up at his or her face, this will work even better.