First you show the viewer three wooden dice of different colors: yellow, blue, red. Each cube has done a small through hole. Now take the box without a lid, which also has two holes - one on each side. Then put the cubes inside the box. The audience can see that the holes of the box and dice are the same. Through the box and dice prodelyvat the strap length of about one meter. For convincing a few times pull it for different ends. Then ask someone from the audience to hold, and yourself... remove the cubes from the box.
Props focus - three wooden cube with sides 120 mm and drilled holes in them with a diameter of about 10 mm
The box should be made of such size that it came and went freely cubes. And now the secret of focus.
Inside the box on the sides and on the bottom make grooves in advance and put them in a sturdy thread. The ends of her print in the side holes of a box and on one of them make a loop.
The cubes should be put in a box. One end of the lace to overwhelm loop thread. And then push it into the hole of the box - it turns out that he runs in the grooves of the first side, then the bottom and out of the holes on the opposite side. The audience absolutely sure that the lace goes through the holes in the cubes.