Optical illusions are neat.

Here we have 4 optical illusions that seem strange or unbelievable but they are true enough. Try staring at the blue birds on the yellow background. After a bit the birds will move slowly.
Next focus on the black dot in the center of the 2 grey circles. Move your head in and out and the circles will turn.
When you look at the 2 blue tables which is the widest table A or B? And when you look at the 2 leaning towers of Pisa which one is leaning more, the one on the right or the one on the left?

The answer to the last 2 questions may seem strange but they are completely true. The 2 blue tables are the exact same size and the 2 towers are leaning the exact same amount. Try turning your head 90 degrees and they might look the same. If this doesn't work for the blue tables hold a ruler up to the screen and you can see that they are the same. So seeing is not always believing.