Imagine you are four years old. A researcher shows you two dolls: Sally and Anne. Sally places a marble in a basket, then leaves the room. While she is gone, Anne moves the marble to a box. Sally comes back. The researcher turns to you and asks: where will Sally look for her marble? If you are four, there is a good chance you will point to the box, where the marble physically is. If you are five, you will probably point to the basket, where Sally left it, and where she believes it still is....