Yarn (approximately 1/2 skein per color) Cording (approximately 35 inches) Scissors Hot glue Superglue
Step 1:  The basic method of creating a tail is by knotting short lengths of yarn to a base cord.  Cut a section of cord approximately 30" long, which will result in the tail ending just about behind your knees of an average height person.  If you would like a shorter or longer tail, adjust the length accordingly.  Keep in mind that your tail will be about 2 inches longer than the actual cord, since you are starting the tying  at the bottom and yarn will hang down below the bottom of the cord.   A bit of superglue at both ends of the cut cording will harden the fibers and prevent unraveling.
Step 2:  Begin by wrapping yarn around one hand as shown.
Step 3:  Slip the yarn off your hand, and you will be left with an oval circle of yarn.  Cut the yarn at one end so that the oval forms a 'U'.  You will be left with strands approximately 7" to 9" in length.
Step 4:  Take two strands and knot them around the cord, starting at the bottom.
Step 5:  Repeat step 3 and 4 until about four inches of cording is left at the top.
Step 6:  You will notice that some empty spaces have formed during your tying.  Fill in these spaces easily by knotting one or two strands of yarn in your fingers (not onto the cording), and using a dab of hot glue to secure it onto an empty space.
Step 7:  Create a loop with the remaining top four inches of cording, and secure the loop with superglue.  Your tail is now complete!
When working with yarn, start at the bottom of the tail and work your way up.  This way the yarn will lay correctly. For a spiky Macavity tail, lay the yarn as a 'V' rather than an inverted 'V'.  (Still start from the bottom). Blended yarn will create a more authentic-looking tail than solid blocks of color. Wear rubber gloves and safety goggles when working with superglue (my favorite brand is "Surehold Plastic Surgery" found at ACE Hardware).  Superglue actually releases visible fumes that can severely irritate the eyes (I was once unfortunate  enough to have this happen to me).  If your fingers or skin become accidentally stuck despite your precautionary measures, a product called "Unglue" or "Uncure" found at local Hobby Shops will help unstick your skin. I always have a bottle  on hand when working on projects that require superglue.