This project was a birthday present for my youngest nephew. I also wanted it to be engaging for older nephews as well so there are three difficulties - the bigger left eye, the smaller right eye, and the mouth. It's easy to tell which hole the ball goes in because each is connected to it's own outlet (e.g. if the ball goes in the left eye it rolls down the left arm). I'm so happy how it turned out and best of all - the boys love it!