The Oldest Cat Flap is Much Older Than Isaac Newton

It's a common bit of trivia that Sir Isaac Newton, along with inventing calculus, also invented the cat flap. While Newton may have made the holes that are still seen in that door (although repaired since), he was far from the first to do so. Ever since cats have lived with humans, they have been demanding interior and exterior access. Cat owners know the frustration of letting a cat in and out constantly, and their maddening habit of standing at an open door, taking forever to decide if they really want to cross the threshold. Cats don't really want to go in, and they don't really want to go out; they just want the door to be open so they have the choice. Meanwhile, humans built those doors in the first place because it's cold outside and we don't care for intruders. So a cat-sized hole, and a flap to keep heat from escaping, is a practical idea that has been around for a very long time. Exeter Cathedral, also known as the Cathedral Church of Saint Peter in Exeter, was completed around the year 1400, and it has a cat flap.

This is just one of several ancient cat doors and cat flaps that predate Newton. -via Nag on the Lake 

(Top image credit: Andrew Dunn)