Now, I really love this one! Larry from Michigan sent me an image I couldn’t miss sharing with you. What we have here is a classic example of “Slanted Lines” illusion, just like the one we published on Monday. The usage of the effect is more advanced this time, since it additionally exploits the nature of the object presented. A seesaw (also known as a teeter-totter or teeter board) is a long, narrow board suspended in the middle. As one end goes up, the other one goes down. When we first see the example below, it looks logical that the right end went down due to heavy triangle positioned on it. The illusion shows just what you naturally expect, but the raw truth is that the seesaw is balanced perfectly horizontal, and doesn’t outweigh – nor left, nor right. You can easily prove this by squeezing your eyes, till you just see the outlines of the seesaw. Thanks for stumbling and sharing this!

Update 1 (02/22/2009): Since yesterday, I have received this enhanced animation from visitor that goes by the name Mr. Anonym. His version might help you in seeing the effect little better. You should be able to spot the moment after which the seesaw gets slanted.

Update 2 (02/22/2009): Alessandro aka SuperSandro sent another example where he modified this illusion. Now the seesaw is actually slanted, but appears perfectly balanced. Here is what Alessandro wrote – “Hi! Today I’m happy to send you this attached file. It’s the same as slanted Seesaw, but rotated for 4 degrees on the rectangle’s side. It seems to be horizontal, but of course it is not.”