Respecting my long-standing fascination with optical illusion, Neil sends along the Pink Dots Illusion.
If your eyes follow the movement of the rotating pink dot, the dots will remain only one color, pink.
However if you stare at the black '+ ' in the centre, the moving dot turns to green.
Now, concentrate on the black ' + ' in the centre of the picture. After a short period, all the pink dots will slowly disappear, and you will only see only a single green dot rotating.