The Display Case is a furniture item in Nintendogs + Cats that can be bought from Modo Home for $2,500 in all versions. It can be placed in one of the four corners in your home. Your puppy might stand on its hind legs and rest its paws on the glass in order to get a better look. Kittens will also rest on top of it.
In all versions, it is readily available.
3DS: "This elegant display case is filled with delicate-looking heirlooms."