Count the number of 'F's in the following text:

           FINISHED FILES ARE THE RE-
           SULT OF YEARS OF SCIENTIF-
           IC STUDY COMBINED WITH THE
           EXPERIENCE OF YEARS


Managed it? Scroll down only after you have counted them!
*
*
*
*
*
*
*
*
*
*
*
*
*
*
*
*
*
*
*
*
*
*
*
*
*
*
*
*
*
*
*
*
*
How many? Most people see three.
In fact there are six - the brain doesn't process "OF".