Hop Step Junk, by Japanese artist Sei Matsumura, is an installation which catches up people’s footstep. According to the difference of their weight and the way they move, the sound of footsteps is turned into rhythm sequences and reflected into visualization.
People just step on one of the stages, make tap dancing-like footsteps and the graphical pattern reacts. If someone steps with enough loudness, the sound of footsteps is recorded and played in loop until another visitor comes.
Better explained in the movie ;-)