How many F’s are in this sentence?

Now count the F’s in this sentence. Count them only once: do not go back and count them again.

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

How many F’s?

There are six F’s in the sentence.

The “average” person finds three.

There is no catch. Many people do not see the Fs in the word “OF”. It has been argued that the human brain tends to see them as Vs and not Fs.