No, that behaviour did not happen “out of nowhere”. A lot of signs were missed before it.
A lot of times we get messages or phone calls from people telling us that their dogs started attacking each other “out of nowhere” or that “they were just playing and all of the sudden they started fighting” or that “suddenly” their dog started being possessive over food/toys/one of the humans in the home.
What may seem like an “out of nowhere” behaviour is actually something that builds over time, and the human missed the signs the dogs ere giving off communicating that they were either uncomfortable or slowly starting to take control of certain situations due to lack of human leadership. This is important to know because the better we understand our dogs, their energy, and their body language, the more we’ll know when to intervene, interrupt, redirect, etc. and then follow through.
Another thing that happens a lot is that we change things in our life (new home, job, relationship, new baby, changes in our routine) and don’t think about the fact that these can changes also throw off our dogs. They feed off of our stress. New environments or any other big changes can cause a stress response in the dog, so it’s crucial to help them understand big transitions.
Learning about dog psychology, canine body language and understanding how the dog’s mind works will help prevent a lot of bite incidents. The dog communicates all the time. We need to learn to listen to them.