This is powerful little piece of mental magic. You will need 3 small slips of paper, a pen and 3 markers (a green, red and yellow.) With the pen, draw a simple traffic light on each of the three pieces of paper. Each of the drawings should feature three circles in a single column, inside a rectangle.
In one of the drawings, color in one of the lights at one end of the rectangle GREEN. In another drawing, color in one of the lights at the other end of the rectangle RED. And in the third drawing, color in the light in the middle of the rectangle YELLOW.