If you want to make catz and dogz play together, you have to have both Dogz 5 and Catz 5 (or Petz 5). then you just choose a cat and a dog and bring them out. Catz and dogz cannot breed.
When you get a cat out from the "Pick a pet" button you chose the pet you want to return.Then your pet comes out to play next to your cats name it has a blue or a pink cat if it's Catz 5 or a dog if...