An amazement and hilarity of the first order.
Two cords run through a tube. On the left side a long string with a black and a yellow woollen pompom at the end, on the right side of the pipe a short string with a red and green woollen pompom.
If the magician now pulls on the black pompom, the yellow one goes up with it, which makes it clear that these two are really connected.
But if he pulls on the red one on the other side, the yellow one also goes up, which means that the string on the left becomes shorter while it becomes longer on the right. So the yellow one must be connected to the red one.
But if the magician slackens his pull on the red one, the green pompom goes down with it, so that the green and the red are clearly connected. Grins and incredulous amazement when the green one is pulled and the yellow one reacts and moves with it.
It looks hilarious when you pull on a string and a completely different pompom reacts to the pull than the spectators assume.
Obviously, each of the wool pom-poms must be connected to the other by secret strings inside the tube.
You demonstrate that this is not so by pulling the tube apart, thus proving that there are no connections at all.
Nevertheless, you can immediately put the two halves of the tube back together to start the game all over again.