[alaskayorkie]

Originally Posted by Nancy1999

I think dogs can probably smell aggression, and if a dog is around aggressive people and then sees the hitting, he associates that with the aggression. So barking to hitting is a learned response. We can't forget that dog's noses are 1000 times more sensitive than humans, and even in humans, smells are powerful things that bring back a flood of memories. Nobody ever pretends to hit me, but Joey barks if someone yells at me.

Interesting answers, everyone, thanks! Nancy, I hadn't thought about that but it makes a lot of sense. It doesn't explain why they'd attack when we're play-fighting, but perhaps as you say they learned the response and are making it to just one of the cues that comes with aggression, the visual one.