Summarize the following:
Decide what shape you want your tail to be, then draw it onto a large sheet of paper. For a cat tail, you could make a long, skinny rectangle that is rounded at one end. For a fox tail, you could make an elongated almond shape instead. It would be a good idea to add a -inch (1.27-centimeter) seam allowance to your pattern at this point. If you don't you'll need to add one later. You can pin the pattern to the fur or you can trace it using a dressmaker's chalk or pen. Make sure that the tail goes with the grain of the fabric, and that the fur ends at the tip, like a real tail. Choose long, fluffy fur for large tails, such as fox or wolf tails. Choose short fur for skinny tails, such as cat tails. Set the fake fur down onto a flat surface with the back side facing you. Slide the tip of your scissors into the fur, then begin to cut along the pattern. Cutting like this will prevent you from accidentally cutting the fur fibers themselves. If you did not already add a seam allowance to your pattern, be sure that you add a inch (1.27-centimeter) seam allowance now. Alternatively, you can cut the pattern out using a box cutter. If you chose a unique shape for your tail, such as a curved husky tail, make sure that you flip the pattern over first. This includes the fur at the tip of the tail. Doing this will prevent the fur from getting caught in the seams, and make cleaning it up at the end easier. Place the two pieces of fur together, with the wrong sides facing out. Sew along the fur using a -inch (1.27-centimeter) seam allowance. If the thread breaks, use a looser tension or switch to a stretch stitch. Leave the top of the tail open. Use a dowel, pen, or knitting needle to help push the end of the tail out further. If your tail had a curved shape, like a husky tail, be sure to cut notches into the curved parts. This will help it lay smoother. You can find bags of this stuff in fabric stores and arts and crafts stores. If you want a bendable tail, consider sticking a thick wire into the tail after you stuff it. Tuck the raw edges into the tail, then sew the sew shut using a ladder stitch. You will be using a safety pin to secure the tail to your costume. If you'd prefer to use loops instead, cut one or two loops out of cording, and add them to the top of the tail before you sew it shut. Alternatively, you can sew a keychain ring or hook to the top of the tail instead. If you added loops of cording instead, you can skip this step and slide the tail onto a belt instead. Focus on the seams where the fur may have gotten caught in the stitch. Next, brush the fur from the top of the tail towards the bottom so that it lays naturally. If you make a husky tail, you will need to comb it at a downward angle instead so that it points towards the outer part of the curve. If the fur is still caught in the seams, use the tip of a knitting needle to pull it out, then comb it again.

Summary:
Create your pattern. Transfer your pattern to the back of a piece of fake fur. Cut the pattern out from the back of the fabric. Cut another piece for the other side of the tail. Comb the fur inwards, away from the cut edges. Pin and sew the tail together. Turn the tail right-side-out through the opening at the top. Stuff the tail with polyester stuffing or fiberfill. Hand sew the top of the tail shut. Sew a flat-backed safety pin to the top of the tail. Comb or brush the fur out.