Human:  "Cat, what is your purpose in life?"

Cat: (condescending stare)

Human: "Come on, what do you do? What do you contribute to the world?"

Cat: "Perhaps your already-feeble human eyesight is deteriorating.  If it weren't, you would immediately recognize that I contribute beauty, and quite a lot of it."

Human: "Well...okay, that's true. But what do you do? I mean, do you make anything?"

Cat: "I do whatever strikes my fancy."

Human: "That's certain.  But you don't make anything. I mean, you don't build buildings or grow food or earn money."

Cat: "Nope."

Human: "So what's your excuse? How do you justify your existence in the world?"

Cat: (yawns)

Human: "That's rude, you know. Hey, look at me...where are you going?!"