The difference between a dog and cat. You play fetch throwing a ball to a dog and he will go, picks it up and brings it back to you, as many times as you want for as long as you want.
Cats play fetch, too, but on their own rules.
I throw a small yarn ball from my bedroom into the living room. She jumps on, fetches it and brings it back, jumps on the bed right in front of face and drops the ball, once, twice, three times. That is it, now she changes the rules and makes something different every time. And I have to. When I find it I throw it away again.