Remove the lid from a shoebox. Set it aside. You can use a different type of box, as long as it has sides at least 3 inches high.
Cut a small rectangle, 1/2-inch from the bottom of the box. Make the rectangle 1/2-inch tall by 1-inch wide. Cut the rectangle from one short side of the box.
Measure the length and width of the bottom of the box. Cut a piece of black construction paper or poster board to this size.
Place the construction paper or poster board on the bottom of the box and lay the prism on top, at least 3 inches away from the rectangular hole.
Turn on a lamp and hold it near the hole from the outside of the box. You will see the light reflect off the prism, to make a colorful display along the bottom and sides of the box. Angle the lamp to the left, then to the right, to watch the colorful display move.