The Blind Spot

Close your left eye and stare at the blue star with your right eye. Get close to your screen, and slowly move your head backwards while staring at the blue star, until the red dot disappears (at about 10 inches / 25 cm from the screen).

Incredible isn't it?! This happens because the light rays coming from the red spot fall on the place where the optic nerve enters the retina - this phenomenon is commonly referred to as your blind spot.
It was right in front of you!