I think it tests more than just words per minute. You can have the ability to type so fast, but if you just mess up once and press one wrong key, it'll target a word other than the one you had your eyes on, and then it can take several seconds before you realize that the game targeted another word, and by the time you re-adjusted yourself to begin finishing that word, all the other words have had enough time to creep up on you and it's just impossible to type fast enough to kill them all, even if they're all small words. Have to be super fact in more than just typing speed, you have to be able to quickly realize you messed up and quickly readjust yourself.