This video above shows various optical illusions that our minds fall victim to. I thought it was pretty cool and we've discussed in class why our minds trick us like this. Optical illusions are also known as visual illusions. It involves visual deception. Due to the arrangement of images, effect of colors, impact of light source or other variable, a large amount of misleading visual effects can be seen. Aside from these effects just being fun and interesting, they let us understand the workings of the brain a tad bit better.
Here's another effect to check out...
The Kanizsa Triangle
A white equilateral triangle can be seen even though it isn't really there. The effect is caused by illusory or subject contours. According to the law of closure, objects that are grouped together are seen as parts of a whole. We tend to ignore gaps and perceive the contour lines in order to make the image into a cohesive whole.