…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.”