Perspective
(Examples drawn from The Haunted Theater)
Another way to push people's psychological buttons is to appear either below or above their normal line of sight. In a haunted house environment, one way to implement this is by putting yourself on a shelf that is slightly above head-height of your victims. Securing yourself with bungie cords or a counterweight system can allow you to loom over them in a very unnatural way. If you set the scene properly, they won't see you until you are practically on top of them, and your mere presence is usually enough to make them cower back into their companions or duck and run. The most entertaining victims will go directly from standing to sitting in one quick drop.
On the other hand, if you put your victims on a raised ramp or walkway, and you put yourself off to the side, on the floor below their normal line of sight, you can freak them out quite easily. Small motions, faint sounds, rapping the floor beneath them, or grasping motions towards their feet will usually have them stepping high and squealing.
Have you ever seen people on TV running around, jumping
on chairs and trying to get off the floor when they see a loose mouse? You can
trigger this reaction on the same level as your victims if you remain low to
the ground in a squat, and scuttle towards them in an unnatural fashion. There
is something in our brains that screams "that ain't natural!" and
causes a flight reaction.