The secret: if you cut 5 pieces of reflective material a certain way, placing them together edge to edge, leaving a hole for your video screen behind, you get a surprise. You think you're looking at a sphere right in front of your face. Unlike a Kaleidoscope that repeats an image in a flat pattern, this curves it into a 3D optical illusion.
This "thing" premiered at the first migratory TouchDesigner User Meeting at SIGGRAPH 2004.