I wear out the heels of my ankle length socks and toss them out when I
find them while folding the clean laundry.  One day I had the bright
idea to put a couple of tablespoons of catnip in the toe of the wholly
sock and then tie a knot that would include the heel area.  Instant
hit with the cats, who love to fight, bite, throw, roll on, chew, and
lick the socks.  The only problem is that they lick the catnip filled
toe end so much that eventually the toe end turns green, dyed by the
"catnip tea" produced by the moisture from all that licking.  I solved
the "ugly green toed sock toy" problem by using dark colored socks the
next time I made some.  I wasn't using those colored socks anymore
anyway, and they were just taking up space in my sock drawer.  
Debra in VA