Reading the comments on forced perspective made me remember an idea I had for a Warhammer 40K (sorry, wargamer background) vignette. I will admit the original idea wasn't mine, I stole it from "Doubled Back" - a painting by Bev Doolittle.
In the painting, one sees bear tracks (in the snow) in the foreground working up the trail (diagonally, left to right in the painting). In the upper right hand corner of the painting, on the trail is a silhoutte of a bear. When the viewer steps in to get a closer look, the silhouette is in actuallity, just a boulder. Upon closer inspection, one finds that the bear is in the brush, in the foreground. The first time I saw it, I was standing up against the wall and actually jumped back a bit when I realized that the bear was "right in front of me." (I grabbed a URL from google that shows the painting -
http://www.google.com/search?hl=en&ie=UTF-8&oe=UTF-8&q=%22doubled+back%22+bev+doolittle Anyways, I had envisioned a vignette in which a trooper was wounded, in mid-collapse. His posture and gaze led one to look for the sniper in the background of the vignette. I'd imagined one could build a structure/paint the shadows such that it appeared as if a sniper were far off in the distance. In actuality I wanted to put the sniper in the extreme foreground, hidden by rubble and debris. In essence, when someone saw the vignette, the would thing that the wounded soldier were looking at his assailant, when in actuality the trauma of being shot had spun him around, disorientating himself and his companions.
Anyways, just a thought. I doubt I'd ever get around to it though, even though it does play into my ever widening desire to play with an audience's perception.