Presented here is the Optical Illusion Ring. Rob over at What is it? pointed it out to me. He said this about this ring.
Optical illusion ring, you can see in the photo that the links on top look thinner than the ones on the bottom, when you turn the ring it appears that they actually grow larger right before your eyes, or get smaller if you turn it the opposite way.
Click the picture to see a video (1.6meg) of the Optical Illusion RingWell the picture and explanation just didn't do the trick for me so I searched the net to see if I could come up with a video that showed this illusion. Once I saw the video I was hooked. This is a very interesting effect. Remember this ring is solid there are no moving parts on this ring. Click the picture to download or view the video.
I found the video here, this shop sells many illusions and magic tricks. You can buy this ring to size here. Unfortunately neither link will make me a dime.