It's a cat thing: When you read a book to tame your cat and the one that ended up tamed was you. (and it's very likely that you did not realice it yet).
Fun Fact: Kitty has been sleeping on top of Papyrus since the beginning. And not for the reason the book said.
After a while, Kitty began sleeping near the head of the skeleton while he was reading.
Papyrus apparently ignored him and did nothing when the cat's tail began to roll over his shoulder.
If he kept quiet on purpose, the skeleton never said. But clearly something changed.
With nothing much to do, since the pup was taking care of Sans, Kitty was really bored.
Inside the house, everything was calm. The only entertainment the cat found was to observe what was Papyrus doing.
He spent most of his free time at home reading the famous book.