A few ferrofluid speakers have hit the market. Beyond just your simple bluetooth speaker, these put on a little show at the same time. They contain a blob of ferrofluid suspended in clear liquid. As the music plays, it pulses magnetic fields through the medium and make the fluid dance. These two speakers seem to be the most interesting. Sovenomund Dancing Ferrofluid Speaker and the CAULO Wireless Ferrofluid Speaker.