1 Cat: Meow! Meow!
2 Isaac Newton: That darn cat. I shall have to invent some apparatus to allow it to enter and leave as it desires without my intervention.
3 Isaac Newton: Some sort of cunning flap arrangement in the door, through which the cat may effect its own ingress and egress.
4 Cat: {thinking} This guy is a much better owner than Schrödinger.

Isaac Newton did indeed invent the cat flap. Or at least popular legend has it - the true inventor is probably lost to history.

Although given how clever Newton was, it certainly isn't terribly far-fetched.