Here is a disk. On one side is a picture of a bird. Here is another disk. On one side is a picture of a cage. Colour them in. Give life to the feathers of the bird. Gild the cage and colour in the sky around it. Then stick them together with glue. Make one disk from the two, a picture to either side. Place a stick between them. Rub the stick between your hands. Watch the disk as it spins before you. Can you see the bird fly into the cage? An optical illusion. The persistence of vision. A trick of the eye. Here is another disk. It is blank. I’ll draw a rocket on it and launch it into the starry sky. Here is one more disk. It is also blank. I’ll draw a robot on it, standing silently against a white background. We’ll stick the two together, the same way as before, making one disk from the two, a picture to either side. With a stick between them that we can rub between our hands. Count down to blast off. The rocket is launching. It spins between our hands and now the robot is its silent pilot.