The cat flap was invented by Sir Isaac Newton

Sir Isaac Newton was a genius, but he was also a bit absent-minded. When confronted with the distraction of his cats wanting in and out of the house throughout the day, Newton invented a pet door by cutting a hole in the door with a swinging flap that would allow easy entrance and egress for his pet feline.

A friend was admiring the invention but asked why there were two holes in the door — one larger than the other. Newton responded that he had two cats — one large and one small — and this would allow each of them to come and go at their leisure.

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