Amaze your audience- and always get laughs!
It's absolutely baffling- and easier to do it than to explain it! You have a tube with four pom poms attached- on one end of the tube is a blue one and a green one, on the other end is a red one and a yellow one. The blue and green pom-poms are attached by a long string at one end. The red and yellow pom poms are attached by a short string at the other end.
Now, the magical fun starts! Show that the blue pom-pom is attached to the green pom-pom. The red pom-pom is attached to the yellow pom-pom. Pull the blue pom-pom and the green pom-pom goes up- they are attached by the long string, remember? Pull the red pom-pom and the yellow pom-pom goes up- they are attached, remember? But now pull the blue pom pom and the yellow pom pom goes up! Pull the red pom-pom and the green pom-pom goes up.
WOW! It looks like every pom-pom is attached to every other pom-pom! And there's always a long string at one end and a short string at the other end. But wait! Pull the yellow pom pom again- now it's connected to the green pom pom by a LONG string too!
But how does it work? The strings must run through the middle of the tube, your audience will yell. So show them! Separate the tube into two parts- there is NO CONNECTING STRING! Gets them every time!