1) Take a worn-out pair of pantyhose. Cut off about 12" of one leg, measuring upward from the foot.
2) Lay out the remaining pantyhose, flat. Put a spoonful of catnip on the seat of the hose. Roll up the hose around the catnip, forming a loose ball.
3) Stuff the ball of hose into the toe of the cut-off leg. Push as hard as you can to make it compact. Twist the top closed and knot it.
4) You now have a ball, a knot, and a loose tube of hose. Fold the loose hose back over the ball and pull it tight so that it's inside the tube. Knot the tube again. Repeat the folding and knotting process until you run out of tube. Tie closed the last end of the hose.
5) Give the ball to your cat, or wrap it as a gift for later. If you have packed the hose tight enough, it will bounce rather well on a hard floor. The pantyhose material makes it easy for cats to catch and hold with claws or teeth. The catnip smell will go through the hose fabric, but under all that fabric it cannot be ripped loose to make a mess.