I got 6 F's the first time. I think it depends on whether you read the words and try to find the F's in the words, or whether you just look for the F-shapes. The explanation only makes sense if you are reading the words and not looking for the shapes. As a programmer, I have trained myself to look for shapes and patterns. Although the human mind may not care about spelling exactly, computers aren't that smart so every single character becomes important.
I found out this the hard way on my very first program I ever wrote. I was just a kid and my parents had gotten me a book to write your own BASIC computer game... It basically had all of the code that you would need to enter in to create your own game, but it would also take out sections of the code and discuss what the different commands were doing. Thus it taught you how to program at the same time as it told you what to type in. Well, there was one line that was sort of long, and on my TI994A (the console / computer I was using at the time) wrapped to the next line (no Windows to scroll to the right on large lines) right at the very end of the line of code. Thus, instead of putting in a hard Enter, I just type in the next line of code. So looking at the book and at my screen, the two looked exactly the same. It was only until I spent extensive time debugging character by character at a time on that line of code (at least at this time, BASIC required line-numbers and the computer was able to state what line-number the error was occurring on) that I was able to find where the problem was. After that experience, I have been very good at picking out coding errors that may be based on just a single character. Later programming courses, other students were amazed when on tests where they had to point out the errors in a sample of code, that I would always pick up on the "missing semicolon" and "mismatching parenthesis" errors.