Actually, there IS such a thing as an anti-gravity device...
You take a slice of buttered bread, and tape it securely to the belly of a cat, with the buttered side toward the cat.
You then toss the cat in the air, and because a slice of bread will always fall buttered side down, and a cat will always land on its feet, the cat will just hover in the air.
Depending on the aga and agility of the cat, and the amount of butter on the bread, the cat will hover anywhere from 1 inch to a few feet above the ground.
Mark