So I have two (somewhat) related questions. 1) Why is it wheel rims (or spokes) sometimes appear to spin backward? Everytime I see this it drives me crazy. I just cannot figure out how a wheel spinning real fast in one direction appears to be spinning real slow in the other direction. 2) So the first question I expect everyone has experienced. This second phenomenon might have escaped notice by most but it is easily reproducible. So if you havn't noticed it before, check it out. Next time you are driving in a car parallel to a diamond wire fence (like you see around playgrounds, schools, junkyards, etc.) take a look at it. Your line of sight should be roughly perpendicular to the plane of the fence (this is not really necessary, but it is the best angle I've found for causing the effect). Don't wreck. The fence should be a quick moving blur and then BAM! you will notice that the diamond shape geometry of the wires gets blown up and superimposed on the passing blur of the actual fence. Kind of like one of those 3-D out of focus pictures. Try it, I swear you will see it to. What is this effect? 3) While we are at it, how do 3-D pictures work also?