In a famous ongoing experiment, subjects are asked to watch a short video featuring three people in white t-shirts and three people in black t-shirts passing basketballs. Subjects are asked to silently count the number of passes made by the people in white shirts. The six players move around, change positions, fake tosses and otherwise make it difficult to track the pass count.

During the video, a woman dressed in a gorilla suit walks among the players, turns to the camera, thumps her chest, and walks out of the picture. Half of the viewers concentrate so fully on counting the passes that they never see the gorilla. (I missed it too.) When you watch the video without fixating on the passes, it is shocking to realize that you could have possibly missed the great ape. (The experiment is online here.)