The frame is open so lightweight objects can be placed inside. The objects then seem to move slowly back and forth, creating a flowing movement comparable to that of a jellyfish.
The illusion is created by strobe lights blinking at 80 times per second, too fast for the human eye to recognize, which are synced with high-speed vibrations applied to the object.
Creator of Slow Dance, Jeff Lieberman, is famous for hosting a television show which appeared on the Discovery Channel called Time Warp. The show used high-speed cameras to capture experiments or other visually appealing events which they then slowed down to show detail invisible in real time.
The Slow Dance appears to have the same effect without the aid of cameras.
It is a simple way that technology is allowing us to see our world as never before.