I had a hard time figuring out how to shoot until i noticed, that I was still in the menu... I thought my goal was to shoot the bats there and that the level selection buttons would be the check boxes of wich numbers I already shot down.
It's a nice twist, that the bullet bounces off the wall, but this also has the potential for rage quitting :D. Counting down the time felt like a key feature. This way you can't simply wait for the best opportunity to shoot.