From seances to pepper's ghost, Halloween is full of tricks and treats. All of the season's best haunts have something in common: a mechanism and physical process. See some of the most iconic haunted illusions and their mechanisms.

Pepper's Ghost

This is an oldschool and classic ballroom trick. A clear pane, glass or acrylic, sits at an angle between the guest and the set. Off to the side, or below, is a second space the guest cannot see. The hidden space is kept dark, so the pane looks empty. A figure is lit in the hidden space, and the pane throws the image into the set. The hidden light dims, and the figure is gone. The main room has to stay dimmer than the hidden one, or the reflection is exposed. John Henry Pepper put this on a London stage in the 1860s, working from Henry Dircks’s apparatus, and the name stuck. Disney’s Haunted Mansion ballroom is the same faucet at ride scale. Yale Gracey built little black-box models with a scrap of glass so Walt could see the ghost appear and fade before anyone cut a pane for the show. Imagineering still uses it, now with video in the hidden room so a figure can move without an actor in a pit.

 

The Scrim

A scrim is a loose weave, theatrical gauze or the black weed cloth from a hardware store, hung flat. When it is lit from the guest’s side and dark behind, it reads as a wall, a painting, or a ceiling. When the front light drops and light is thrown behind it, the cloth goes transparent. The Stretching Room in the Haunted Mansion does this. The ceiling looks solid until the room lights drop and the attic above is lit, and then the view is through the cloth at what was always there. Wrinkles ruin it. The cloth has to be tensioned even, and no stray light can hit the hidden side while the wall is meant to hold. A small version is a picture frame over weed cloth, a figure in a black box behind it, and a lightning cue that swaps which side is bright.

The Floating Head

The old carnival head on a table is a mirror set on a diagonal. The body sits behind the glass, where the guest’s line of sight cannot go. What shows above the mirror line is the real head. What should be a torso is a reflection of the empty tabletop or a painted board, so the chest is missing and the head seems to rest on nothing. When the mirror is clean and the lighting matches on both sides of the line, the seam disappears. A phone, a fingerprint, or a brighter lamp on one side gives the edge away. The form is a pane at an angle. The function is a body the eye agrees not to see.

The Séance Table

The Victorian parlor trick that still gets called a séance is usually a light table and a dark room. Hands rest on the top. After a while the table creeps, tips, or knocks. In 1853, Michael Faraday tested whether the wood was being moved from below or from the hands on it. He stacked cards on the tabletop, weakly stuck together, and marked them so a shift would show which layer moved first. If a force under the table had pushed, the bottom card would have led. The top card led. The hands had moved first. The sitters were not faking on purpose. In the dark, with a shared expectation, small unconscious pushes add up, and the table answers. A later version of the same test puts a pointer on a loose board so each person can see when their own hands start the motion. When the sitters can see the pointer, the table often stops. The form is a piece of furniture with too many hands on it. The function is a movement the group produces and then misfiles.

The Blue Room

This one is rarer than the pane in the ballroom, and it was built for a fright. In the late 1870s a London stage held a small room painted and dressed entirely in one color, usually blue, with a figure in a matching costume. Under ordinary light the person was plainly there. When the light on that room shifted toward a color that the blue cloth and paint would not return, the figure dropped out of view and whatever had been waiting in a contrasting color, often a skeleton or a second actor, took the stage. Audiences in 1878 left convinced they had watched a transformation. The form is a set and a costume locked to one pigment. The function is a light that the pigment can no longer answer. It sits in the same century and the same shop as Pepper’s Ghost, and some versions borrow a glass, but the scare is the color match, not a reflection from a pit. A fairground copy of it turned a girl into a skeleton under the same principle.

The Asrah Levitation

An assistant lies down and is covered. The covered shape rises, holds, and settles. When the cloth is drawn off, the person is gone. The version called the Asrah, credited to Servais Le Roy around 1901, does this with a light wire form that is waiting behind the couch. While the cloth goes on, the form is brought over the body and the person leaves through the furniture. The wires and the cloth rise. The person does not. When the cloth is pulled, the wires are thin enough to vanish against a busy backdrop, or they are whisked up with the fabric. What the eye tracked was a shape under a sheet. The body had already taken another exit. It is the séance table’s rude cousin, and it belongs in a haunt because the scare is the moment the sheet is empty.