Friend or Foe?

These are our dogs, Sigh and Rhoda. From these pictures, you would think that they hate each other and fight to kill. But they are best friends and love to "play fight". It actually looks like Sigh could bite Rhoda's head off, and he probably could, but Rhoda is usually the perpetrator and goes after him, biting his ears and growling like she's soooo big. It's a good thing Sigh is a good sport.