Sometimes the faces don't register that you've clicked them for some reason, but I like the idea of target/distractor items and looking for the right one. In this particular case, you have one target numerous times and a distractor item. Since there's 1 of each, it's very easy for players to identify the one they need, and dismiss everything else. This leads to a very quite search because they are guiding their search to the item they need, and automatically processing out the other item. You can see the same sort of thing with colours. If a player has to look for blue items over red, the red will get filtered out.
Have a think about how you can add challenge to this experience. Also once the player clicks all the faces, the game stops. There needs to be some sort of win screen or way to progress in the game. The score is nice, but the score in this case will always be the same for all players. Which means there's no highscore option for replayability. How can you modulate this? Maybe some sort of time attack that makes the player want to beat their own time?