You may have seen this before—it’s been kicking round for years—but the idea behind it never ceases to amuse me. This little test demonstrates how our mind concentrates on just the important details, which is something to keep in mind when proofreading!
How many Fs are there in this sentence?
FINISHED FILES ARE THE RESULT OF YEARS OF SCIENTIFIC STUDY COMBINED WITH THE EXPERIENCE OF YEARS.
Scroll down for the answer…

The brain cannot process ‘of’. Most people answer three, an answer of four is quite rare. If you said six first time you are a genius and a born proofreader and if you said seven then you should have gone to Spec-Savers!