What's a cat's favorite book?

This joke purr-fectly plays on our expectations with a clever double entendre. When we first hear "happy ending" in the context of a cat and a book, our minds naturally go to the satisfying conclusion of a story, where all the characters are content. It's a wholesome image, fitting for our furry friends (Review) who often seem to live lives of blissful contentment.

However, the punchline delivers a delightful twist by tapping into another, more adult meaning of "happy ending." This phrase is a well-known euphemism, often associated with certain illicit services that are decidedly not found in your local library. The humor springs from this sudden, unexpected shift from innocent animal preference to a surprisingly risqué suggestion, creating a moment of playful shock and amusement as our brains make the naughty connection. It's the unexpected subversion of an innocent setup that makes us chuckle.