Incredible timing, Platapus
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Edit: Steve, you'd be surprised how close you hit the nail's head there. As I said, I occasionally work in a kennel and often we just have to put two dogs in the same cage. It doesn't take long for them to decide which one humps which. But that's still pretty tame, since it's normal for them.
On the other hand I have seen cases that are no different from our form of bullying. One of the dogs has simply established its place in the hierarchy in such a way that the other one has refused to go back to their cage after they have been left out for a while. And in some cases the dominant dog hasn't even let it back in.
Dogs are fascinating.