I have 2 Chiweenie brothers. Both have been raised EXACTLY the same. One is ALWAYS docile & goes with the flow. The other is the polar opposite. He can be loving, licking, happy. A second later he's aggressive, to the point that he growls if you try to pick him up or move him. It's a constant back & forth thing with him. I am beginning to think that he may have some sort of mental disorder; anyone else have any insights? Thanks in advanced!