An "illusion" that has been around for years, rings that roll. What else can be said? Grand kids love them.
Very short garage floor video is here: http://www.youtube.com/watch?v=HLmnVpQsMtQ&list=UUv_zm49u-RjnCJVwhUO-ecA.
Designed using Sketchup 8 and printed in PLA on a Replicator2 using Makerware 126.96.36.199. Printed mine at Makerware "High" resolution.