Two Dogs Play Fighting (Playing Rough)

My 3-year-old sibling dogs play fighting. At first, I was afraid some of their play sessions together were too rough -- but my veterinarian assures me that the behavior is completely harmless. Two dogs (especially siblings from the same litter, as mine are) will play very rough together at times. As the parent of two or more dogs living under the same roof, you will eventually learn when they're playing and when they mean business.