Bennett describes a model that illustrates how stars "wobble" when a planet orbits them. This wobble is because, as you know from Newton's 3rd law, the planet's pull of the star equals the star's pull on the planet. Star and planet orbit a common center of mass that is offset from the center of the star, so it moves with a small orbit around the center of mass.
To do this assignment you can use a pencil or a ruler or straight piece of wire. Tie a heavy object to one end and a much lighter object to the other. The heavy object represents a star and the light one a planet. Tie a string around the point on the pencil, ruler or wire that allows it to balance...the pencil or ruler should be horizontal. Now tap the light object to get it to "orbit" the heavier object. Observe and report what you see. Make a connection between the motions you observe and the detection of extra solar planets. Imagine that all you can see is the heavier object...what kind of motion does it have? What can you figure out must be happening to cause that motion? Write several paragraphs explaining what you did and what it shows.