Having met up with your friends in a café, you ask one of them to choose a card. Take some then cards out of the deck and have your volunteer lose the selection in the small card packet and shuffle it. With these cards, form a circle in the centre of the table. Next, place a glass of soft drink with a straw in the centre of the circle. Say that the straw will be the periscope of a submarine (the glass) which has to find the spy boat (the chosen card). You concentrate hare and, incredibly, the straw starts to slowly move around inside the glass. After a few moments, it stops, and you all realize that it has stopped in front of a card...yes! It's the chosen card! And this is only the many uses for this revolutionary prop!