I found an example of these bookmarks with the Wicked Witch's feet poking out of a book and thought my students would enjoy making their version of someone being squished in a book. They loved the idea of creating monster feet or animal feet.
Start with a cylinder of clay and bend the cylinder into an L shape for the feet. Using small clay tools, design details like toes, shoes, pant legs etc. Remember that if you are adding any parts on, you need to scratch-to-attach them on. When you are done forming your legs, use a knife to cut a slot perpendicular to the feet about half an inch deep into the legs. As your clay dries be careful to keep the space in that slot open, if it gets flattened, you won't be able to attach your cardboard bookmark. Let your clay dry and bisque fire it, then glaze your pieces as desired and fire again.
When the clay parts are finished, cut a piece of cardboard that is about 1 1/2" wide by about 5" long. Put a small amount of glue into the slot and slide in the cardboard. Let dry while you start reading your favorite book!