This is a coffee table that I built with a fluid-filled disc on the top. The disc can be rotated freely, and the speed and direction of the rotation will cause the fluid to swirl around in different patterns. The fluid is called rheoscopic fluid -- it is designed to show the intricate patterns in turbulent fluid flow. More here: http://benkrasnow.blogspot.com/2013/01/rheoscopic-coffee-table.html