I have a young chihuahua and she likes to play with balls. You can get yellow balls that look like mini tennis balls, or there are rubber balls with pebbled or uneven surfaces that cause the ball to bounce in erratic directions. My chi likes both, and we throw them in the house. Of course this also requires you to train "fetch" so the dog understands to come back with the ball. Always reward your dog when it comes to you, this is always a good behavior, even when they were supposed to stay. With balls, be sure it's big enough it cannot be swallowed, but small enough the chihuahua can grasp in its mouth.