Matchbox

Effect: A matchbox obeys your commands.
Secret: Run a thread through the end of a matchbox drawer (see figure 1). Put a small eraser or a block of wood in the drawer on top of the thread (see figure 2) then close the box. You are now ready to show the trick. Hold each end of the thread, with one hand above the other. The matchbox should be near the top of the thread. If you hold the thread loosely the box will slide down the thread but if you secretly tighten the thread the box will stop (see figure 3). With practice you can make it stop or go at your command.