I witnessed something this weekend at my daughter's house. She owns a Pit Bull. They call it some type of terrier, but my eyes see a Pit. She is strong, muscular and one of the sweetest animals you could hope to see. When my young granddaughter visited a few years back you have never seen an animal that transformed and became gentle as a lamb around her. She even got up on the couch and put her head that the little girls lap. I think the biggest fear a burglar would have is getting licked to death. However, she has an internal hit list for certain other dogs. There doesn't seem to be any reason (she was a rescue dog) but most other dogs she just ignores but there are a few that she gets absolutely aggressive when she sees them.
Now my story, my daughter is very cautious about making sure that she keeps her on a leash when going out for a walk, her husband on the other hand will go out in the yard and just let her run loose. She hardly ever moves away from him UNLESS one of the other "marked" dogs goes by and then she goes on a fast run toward that dog. My daughter has told her husband about a gazzion times to not do that. The have a very long leash just for that purpose. He does it anyway. He took her outside while I was there and all of a sudden she spotted one of the target dogs and head out at full speed. He had to call her very loudly and angerly to get her to stop and come back, but fortunately she did. He was very angry with her but strictly verbal not physically. He took her by the collar and brought her back in the house angerly yelling at her calling her bad girl, etc. Things that one would think a dog would not understand anyway. She came in and that is when I noticed her demeaner was different. I've never seen her look so sad and concerned that she made him mad, or whatever she figured out he was mad about. Her eyes were filled with sadness and concern that she had just lost a friend. It was horrible to watch, but I will never again think that animals do not have emotions. She has one of those rock hard tails that Pits are also famous for that is usually moving in a blur of motion and actually once put a dent in their kitchens metal trash container. This time is was still, not a single movement and when my SIL came back in and sat in his chair she looked up at him with a look that would melt your heart. She knew she did wrong, I'm not sure she understood exactly what, but she knew she was in more or less a time out. Even a person like me, often accused of being dead emotionally, was almost overwhelmed with concern.
My daughter realizes that if that dog, being a Pit, did any harm to anything or anyone, she would be put down because of her species. We all wish there was a way for whatever triggers that aggression could be harnessed it would make life a lot less problematic, but nothing seems to stop it. This isn't the first time she has done that. Nothing happened in the end but someday it very much will. That is the problem with a rescue, you have no idea what their previous life was like and what happened that was permanently imbedded in the animals brain.