'(..) Sir Isaac Newton, renowned inventor of the milled-edge coin and the catflap!' 'The what?' said Richard. 'That catflap! A device of the utmost cunning, perspicuity and invention. It is a door within a door, you see, a ...' 'Yes,' said Richard, 'there was also the small matter of gravity.' 'Gravity,' said Dirk with a slightly dismissed shrug, 'yes, there was that as well, I suppose. Though that, of course, was merely a discovery. It was there to be discovered.' ... 'You see?' he said dropping his cigarette butt, 'They even keep it on at weekends. Someone was bound to notice sooner or later. But the catflap ... ah, there is a very different matter. Invention, pure creative invention. It is a door within a door, you see.'