"Although animals are not people, they do deserve to be treated humanely."
Have you ever watched a cat when it catches a bird or a mouse? They "play" with it (aka torture it) before they kill it.
No they don't.
While domesticated cats certainly retain much of the predatory nature of their wild "cousins", enough of the killer instinct has been bred out that a quick and certain kill is not assured. What YOU describe as "playing" is actually the cat fluctuating between two instinctive impulses: to kill OR to ignore. If the prey remains motionless, the cat will likely ignore it. But if the prey moves, the cat will reflexively attack (albeit with much less competence than wild felines).
That's why cats sometimes chase their own tails or like to "play" with string or yarn. They're instinctively programmed to attack something that shape that is moving: snakes!