Wrap the yarn around your book several times, then carefully pull it off, making sure the shape is intact.
Take a small piece of yarn and tie off the top of the loop then cut the bottom loop. The yarn should hang freely now.
About an inch and a half from the top of the ghost, take another small piece of yarn and tie around the yarn to create a ghost head.
Using the black felt, cut out two triangles for eyes and a circle for a mouth. Carefully hot glue them onto the head of the yarn ghost.
If you choose, thread black ribbon through the top loop of the head so you can hang the yarn ghost.
Repeat these steps until you have your desired amount of yarn ghosts.