This is an interesting door hanger cat toy.

The Fling-ama-String is an automated-battery operated cat toy.  It can be placed on any standard door knob to give your kitties hours of fun.  It works by flinging out a string and quickly pulling it back in.  This of course will drive your cat crazy, trying to catch and hold onto the string.  The device comes with a security strap to wrap around the bottom of the door so even a very strong kitty won't be able to pull it off from the door.  It has two speeds of operation that will entice any kitty to play with it.  The Fling-ama-string requires no assembly and runs on 3 AA batteries.

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