The 'in' words all have something in common that is not true of the 'out' words. The order that you click on the 'in' words does not matter; just avoid the 'out' ones.
For each shot that you get in, another 'in' word will come back at you to help you make your next selection. Think carefully about your shot selection, or you will lose the rally! (The secret rule is revealed if you get to the end, then click ~~~CLICK TO FINISH~~~ to win the game.)