So you know those little cat toys that are shaped like mice this is the same thing except a lot stronger. Basic materials are used and anyone with a cat can make this. It took me a few days because on of my cats stole it and I couldn't find it; until it appeared in the water dish a few days later.
I am entering this in the full spectrum contest so please vote.

Step 1: Gather Materials

You will need:
100% wool yarn (I used one of those tie dyed ones in a camo print)
Water
Dish soap (I used Dawn)
Scissors
Yarn needle

Step 2: The Body

Take your barn and start rolling and wrapping into a small ball. This one is about an inch in diameter (3.25 cm). Cut the ball off of your main yarn and tread it through your needle. Pull the needle through the ball to secure the yarn, so when you start felting it doesn't come apart.
This part doesn't have pictures, but I hope to add some.

Make the water from your faucet as hot as you can stand. Get the yarn ball super wet and add half a drop of dish soap to it. Then start to roll the ball gently in your hand till you can add more pressure and it won't fall apart. Mine felted in 7 minutes. It will get a little smaller and won't come apart. Once it felted to your satisfaction make the water as cold as you can stand it while running out of the tap. Rinse the ball with this water; it shocks the fibers locking them in place.

Step 3: Extending the Body

So this part is a little confusing.
Wrap two layers of around the ball. Then put your middle finger in the back of the ball and wrap about 5 times around finger. Now slip your ring finger behind your middle finger and wrap three more times.
Now these loops were made to help extend the body into a tear drop shape. Wrap perpendicular to the loops you just made to secure them in place. Next, wrap like you would for a normal yarn ball, but making sure it stays in a tear drop shape.

Step 4: Felting Time Again

The first picture is what the ball should look like before you start felting it.
Then felt in the same way as the first one. Mine took about 10 minutes. Make sure to be gentle to guarantee the teardrop shape stays intact.
The second and third pictures are after felting.

Step 5: The Tail

Every cat toy should have a tail. Cut a piece of yarn three times as long you want the tail to be. Made mine about 4 inches long so I cut the string 12 inches long. Tie a small knot at one end and separate into three strands at the other end, and braid it. Once the braiding is complete tie a small knot at the other end.

Step 6: Attaching the Tail

Cut off a four inch piece of yarn and thread through the needle and through the knot or loop on the tail. That's the first picture. Then push the needle through the narrow end of the body, so both the tail and the body are attached to the four inch string. Tie the string together as tight as you can. I used a double knot. That is the second and third picture. Then knot it around the tail to be extra sure it doesn't fall apart.

Step 7: Felting the Tail

Just like the other steps we need to felt the tail. Just be a little gentler and and take more time to ensure the mouse has been felted right. The picture is what mine looked like after felting.