What Swat?

There is a sharp difference of opinion as to the most useful invention ever invented. Some hand it to the wheel; others favour the bottle. Certainly both have served to make the world go round. It is to be hoped that the invention of the gun will not make it go flat. Apropos of invention:—

Twinkle, twinkle little 'plane
How I wonder what we gain,
Up above the world so high
Dropping terror from the sky