Sir Isaac Newton accomplished some very important things in his life. He came up with a modern version of calculus and he described the laws of gravity. But he also is said to have invented a very useful thing for cats. It is for the invention of the cat door that Newton is most fondly remembered by cats.
The pet door is found convenient by many owners of companion animals, because it lets the pets come and go as they please, reducing the need for pet-owners to let the pet outside. They also help ensure that a pet left outdoors can safely get back in the house.
Whilst at the University of Cambridge, Newton's experiments were constantly interrupted by his cats scratching at his office door, so he saw two holes in his door: a large hole for the mother cat and a small one for her kittens.