The canine ladder of aggression is a simple visual aid explaining how aggression escalates in dogs. Although the behaviours would manifest differently, I suspect it's not that different in other species including those of us calling ourselves Homo sapiens. It's pretty simple. It starts relatively peaceful ~ for example a lip lick or turning away from the stressor. If the stressor persists, fear and anxiety increases and aggressive displays become more obvious and more serious such as a growl, air snap or bite. All dogs are different and each dog has their own individual tolerance for stress. Also, some dogs have been punished for showing displays that are by all accounts non-violent (e.g. a growl). This can cause them to move up the ladder to a more obvious and serious display of aggression. If your dog could speak it's likely they would say something like this about a stressful situation ~ "Hey, this thing is making me feel uncomfortable. I really want it to go away."
Canine Behaviour Tip #2: NEVER punish a growl. It's information. That simple. Nothing personal. No need to feel embarrassed or upset. It's your dog's way of saying "I need your help before my fear / anxiety escalates up the ladder of aggression."