"Genie, I wish that this person becomes a cat. Now you're going to learn what it's like being someones pet." The genie says, "As you wish, my mistress" and fires a bolt of magical energy at you. At first nothing seems to happen, but then, fluffy tan hair starts coming out of your skin, quickly covering your entire body with a pattern of darker stripes on your back. You watch your fingers as their shrink and thicken into tiny paws, small black claws growing out of your former fingers and forming leathery pads on the bottom. Shaking off your shoes and socks, you see the same has happened to your toes. Your hands and feet further merge into flat paws, your legs quickly shrinking and thickening to support a quadrupedal position as you fail to maintain your balance and land on all fours, your legs now just as long as your arms.
You feel your face contorting as it stretches out a bit into a feline muzzle, your nose now flat and pink and teeth decreasing and extending within your mouth until you are left with little more than a pair of cat fangs. Your eyes burn tremendously as everything seems to go extremely bright, acquiring a green color and pupils quickly turning to slits to accomodate to light levels. You can feel your ears bend and twist as they gain more of a conical shape and move up your head, quickly turning them into extremely sensitive hearing devices.
Now that your head and limbs have changed, your entire bone and muscle structure contracts into a far more suitable shape for walking like this, and you can feel the cracking of bone going down your entire spine until it reaches the end...as flesh and bone starts extending outwards, quickly forming a rigid, tan feline tail that you are able to impulsively twist with remarkable ease. Finally, your body size decreases steadily, shrinking you out of your clothes until beneath an empty heap of clothes a mewing bump is all that's visible - you.
You move out of your clothes, and you look up at your ex-girlfriend, who now seems gigantic. "And now, my dear", she says as she kneels near you and picks you up, "you're going to learn what it means to be a cat - MY cat." As she holds you, all you can do is mew in protest.