My hypothesis was that the dog will go after the moving ball, not the ball that is just staying in place. When we tried it, the dog went after the moving ball. When we only put down the ball that wasn't moving, he went after that one too. So, my hypothesis was wrong. He will go after any ball.
Try this experiment at home. It's a fun project. Please subscribe to our blog and post a comment to tell me what you find. You can subscribe by using the subscribe thingie on this page. You can post a comment by clicking on the comment link at the bottom of this post.