Please be careful encouraging it. My old roommate thought it was funny to get my puppy at the time to chase a flashlight. Four years on we still cannot break her of the habit, and its become an obsessive behaviour. We have to bring her inside because she'll chase shadows in the yard to the point of exhaustion. She'd chase car headlights given the opportunity. She chases reflections from anything. She opens and closes doors to chase the reflections from the windows. She barks and digs at shadows, lights or reflections on the ground. We can't even wash dishes with her in the kitchen because she chases the reflection of the sunlight on the water. Its pretty much ruined her SAR career, because she can't work at night with flashlights around.