I am not a trainer or behaviorist and I don't play one on tv. But, in my opinion, if Zeke was stepped on, I can see why he was not happy. It could have hurt. I muzzle my dogs (except for the toothless one) when I am not home. I also permit my dogs to growl at each other - within reason. They need to be able to communicate without having to resort to biting. Zeke didn't bite, though, and he could have if he wanted to. What size pen do you keep them in?