If you have at least one dog and at least one cat, and you leave your 3DS unattended for a while, your cat might go outside. Tap the kitten's photo in the lower screen to get him or her to come back. Your cat might return bringing a gift to you.
How to Get your Cat to Go Out
If you leave your 3DS open while you are in your home in the game, and you leave it open without pressing any buttons, your kitten might go outside. Be careful not to get in range of the 3DS camera, because the game uses face recognition, and your kitten might not go outside if it sees you in the camera.
How to Know if your Kitten Went Outside
Normally when you leave the game unattended, the game will take turns focusing on each of your pets (you can see what this "focusing" looks like when you tap on one of the photos of your pets in the touch screen: the background turns green and a cursor appears around the pet photo.) If you don't see the game focus on your kitten for a while, that means that it has gone outside.
How Long does it Take for the Kitten to Go Out?
If you leave your 3DS unattended as described above, it should take about 30 to 45 minutes for your kitten to go outside.
How to make your Kitten Come Home
If your kitten has gone out, just tap on the kitten's photo in the touch screen to make it come back. When the kitten returns, it will bring a gift for you.
Gifts that the Kitten can Bring