What is it about tennis balls that I can never get enough of? I personally only really like the yellow ones. I feel I need to have one wherever I am. Even just sitting next to me, knowing one is there makes me more comfortable. I can keep retrieving a tennis ball for as long as someone wants to throw it for me. I don't feel right swimming unless I am going to get or have a tennis ball in my mouth. The sound of a new tennis ball can flipping open makes me drool. I wonder if this is some type of medical condition. Obsessive Ballpulsive behavior?