I found this video a few weeks ago and thought it was really interesting. This experiment focused on change blindness and how the brain focuses on key aspects of the scene, yet omits certain visual changes. Subjects would enter a waiting room and go up to one experimenter at a counter to fill out a consent form. After they're done, the experimenter ducks down behind the counter to put the form away and a second experimenter takes his place. 75% of people didn't notice the change. It really makes you think how much you are really seeing, and how different another person's perception of the same event may be.