Mind trick

Try this, its actually quite good. But don't cheat! 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!

OK? How many?

Three? Wrong, there are six - no joke! Read again!

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

The reasoning is further down.

The brain cannot process the word "OF".

Anyone who counts all six 'F's on the first go is a genius, Three is normal.