Ask the kid to make the phone. Prepare two empty matchbox without the outer part, two matches and thread. In the center of each box we need to make small holes to put them in the thread and bind to the two ends match. The phone is ready. Give one boxes-tube baby, and the other is to hire yourself. Depart from each other so that the thread is stretched. Ask your child to bring boxes to the ear, and in his tell him some greetings. Exchange roles. What happened?