My dog Lucy got into her first serious dog fight yesterday with my daughter's dog. They have played with each other since Lucy was a puppy and this is the first time they have gotten into a fight this bad. I think it started when my daughter's dog got her front paw stuck in her collar while they were playing. I'm guessing she growled or nipped at Lucy to leave her alone because she was pretty helpless and scared. Something set Lucy off ahd she tore into the other dog. She had the dog pinned against the couch and my son-in-law. There was actually fur flying. I grabbed Lucy's back legs and pulled her off. She immediately stopped and showed no further aggression. My daughter's dog had a little bite mark on her muzzle and a pretty bad bite on her back that went through the skin and left two holes. My daughter's dog was pretty upset, but Lucy acted as if nothing had happened. It was like flipping a switch. One minute she was fighting like crazy and the next she was looking for something to play with. Do I need to be concerned? Do dogs carry grudges? Has Lucy turned dog-aggressive?