A Budding Engineer

Our 22-month-old daughter made this configuration, completely spontaneously.  They are made out of little square board books someone gave us.  I, being the model of positivity and open-mindedness, warned her as she was putting the top book on, "It's gonna fall!"  But to my amazement, it didn't (right away).  I went to get the camera, and by the time I came back, it had fallen somehow, and she managed to get the fourth book on top--again, and it stayed.  I can't believe she did it twice, and the second time it fanned out really beautifully.