The device is a modified camera -- in this case, an old manual Minolta SLR. A flashgun fires through the camera in reverse, from the back. The flash picks up the image of a slide inside and projects it out through the lens and onto any surface.

The trick is in the triggering. The Fulgurator lies in wait until an unsuspecting photographer takes a picture using a flash. When the device's sensor sees this flash, it fires its own unit, throwing up an image which is captured by the hapless photographer's camera while remaining unseen by the naked eye.

When I first saw this a few days ago, my mind immediately leapt to an old episode of Future Weapons on The Discovery Channel where tanks were fitted with armor that would explode outward right before an incoming missile was going to hit. This device, however, brings copious amounts of joy, not destruction, to its user. Think about it - you can project whatever image you want onto other people's photos. How furious (or overcome with laughter) would you be if you got home from a vacation, only then discovering that all of your photos of Siegfried & Roy were framed with "I CAN HAS CHEEZBURGER"? Ceiling Cat is watching you fulgurate, indeed.