The Piano is a furniture item in Nintendogs + Cats that can be bought from Modo Home in all versions for $4,000 once it has been unlocked with 7,000 Owner Points or by playing 24 days. It can be placed in one of the four corners of your home, and kittens will sit or walk around on it. If your kitten walks around the piano keys, the piano will make sounds.
3DS (NTSC): "Kittens enjoy pouncing around on the keys of this piano."
3DS (PAL): "Pets love the sound of the piano. Kittens might have a go on it too."