A lot of people have been leaving the rat tail out. The rat tail cord is simply to give the piece more shape. When you start the beadwork you will be working around the rat tail cord. As per #1 on page 66 it says to tie the beads into a circle around the 1mm cord. and work odd count peyote stitch around the cord. Once you have the beadwork done then you are to sew through the cord several times to make sure it is connected to the beadwork. Personally, I would leave the rat cord out. You can add it if you want but your piece should be stable enough to wear with the cord. Hope this helps.