The problem isn't wether this would create some sort of perpetual motion machine,
which it probably would, but how you'd harness the motion to do something useful
with the generated energy.
The cat/buttered toast unit will certainly hover above the ground, spinning eternally, but in order to add propulsion, you need to install a new unit, powered by tomato sauce and expensive white Italian shirts.
First dress the cat in your most precious and virgin-white shirt. Then strap the buttered toast to his back - he should hover above the ground. You now need to carefully affix a mechanism which propels tomato sauce in the direction you want the cat to travel. (It should be relatively easy to get the spinning motion of the cat/toast unit to power this mechanism). The cat will instantly be propelled in the direction of the tomato sauce! Replace the wheels of your automobile with four of these cat/toast/white shirt/tomato sauce units and you have an excellent hover-car which should never need refuelling!
The principle behind this, of course, is that expensive white shirts cannot resist being splattered with deep red tomato sauce. My mate Neal came up with this whole concept.