Nintendogs + cats on the 3DS. What do you do? Ohmigod, you totally pet them and rub their bellies and scratch their heads and make them super happy! Unfortunately, there wasn't much else to do in the extremely restricted demo offered by Nintendo. In my short time with it, I was able to notice just two things: the graphics really are a generational leap over the DS and cats are so much harder to please than their canine counterparts.
Calling your Nintendog is rather simple, and the "gameplay" offered in the 3DS version is not too different from its predecessor. You can use the stylus to pet it and you can even use swipe gestures to have it roll over. Rub enough in the right places and stars will come out of the dog's eyes, indicating its rather happy disposition. You can then use a variety of toys and accessories with your pet. I quickly gave him a cowboy hat. Because how could you not?
Unfortunately, the cat was a bit more finicky, requiring more attention and effort when calling. You can tap the cat icon on the touch screen to call her over, but she seemed totally okay with not responding. Even after a vigorous head scratching, she never seemed too enthralled by my presence. I'll win you over yet, cat!