Mia sometimes does a kind of growl when playing tug but it is not aggressive. I have only ever heard her growl in a warning way in one circumstance and that is if my kids try to take a bone out of her mouth using their mouth. (I know that is a really stupid thing to do but they are teenage boys and thought it was funny. They have stopped it now). You can take anything away from Mia, even the bone out of her mouth, if you use your hand. Mia has never growled or barked at another dog in all the time we have had her. She has barked at people but that is when she wants to play with them or they are outside the gate. Mia must know what a warning growl is as she used it to tell the boys not to use their mouth to take her bone. Why doesn't she warn under an other circumstances?