Our little Boo, who constantly instigates the other dogs, has twice had a few stitches on her left side. Both times Buddy got irritated with her, and, in a blink of an eye, nipped at her!
In our house, we know why this happened: greyhounds are trained to be competitive and aggressive racers. When all 3 of ours get to running together, that is the only time they get mad at each other! They growl, nip and bump into each other. After Boo getting two ow-ies, we know either run them one at a time or muzzle them if they are outside for a long period of time.