In case any of you wanted to make a perpetual motion system, here are some ideas:
1. Toast always lands butter-side down
2. Cats always land on their feet
so, tie some buttered toast to the back of a cat (butter away from fur, obviously). Pick up the "buttered cat" and drop it*. The cat can land on its feet or the toast can land butter side down, but not both. Stuck in this contradiction, the cat will hover in mid air, and possibly start to spin.
This may fail if the cat manages to eat or dislodge the toast.
Some people have suggested that this is what aliens use to make their flying saucers fly without apparent rocket boosters, engines, etc. The sound of many purring cats would explain that humming noise that UFOs make, too.
* This step has not been approved by the RSPCA
This is an old joke that has been told a million times before and I see no reason why it should be told again here.
Locked.