I got my cats da bird toy and they love it. My only concern is after about 10 minuets running after it they are panting and breathing shallow. Is this ok? Am I playing them to hard? Will they stop on their own when they get to tired or will they play themselves to death? They are 1 year old and 7 months old. They are not overweight, this is the hardest they have played before though. Any input?