This cheat works for both Catz 2 and Dogz 2. First, adopt a pet that is Completley identical to the pet you want to bring back. Bring it to your playpen and select the "Petz" section in your tool bar. Select "Copy Petz" and click on the pet you just adopted. Instead of clicking save, choose either "Runaway Pets" or "Returned Petz" depending on wether the pet you want to bring back ran away or was returned. Don't press enter. Instead, go back to where you began from (Still in the "Copy Petz" screen)and select "Adopted Pets". If you did this correctly so far, all the names of the pets you currently own should appear on the screen. Press the "Save" option and you have your pet again! ;)