Those of you who have been reading along here for a while may remember Rainer, the shy, foxy-looking German shepherd who we fostered for a little over four months.
Rainer was so gentle toward us and toward Pyrrha, but he had some serious territorial aggression toward other dogs, and he once tried to kill (actually kill, not just scare off) a potential adopter’s male dog — a terrible, terrible day which resulted in several ER visits for humans and dogs. He also showed lots of aggression toward baby Georgia when she came to visit, and he was always riled up by seeing other dogs on walks.
For this reason, when he was adopted by a young Marine, we counseled him to be extremely cautious with Rainer and other dogs and to continue the positive reinforcement training around his fears. That said, Rainer certainly had the potential to be good with other dogs, because he loved Pyrrha, and she loved him; they never had a serious quarrel.
Just last night, I got a text from Rainer’s adopter, who said that he was doing well — and to my shock and delight, Rainer had a puppy sibling! An 8-month-old German shepherd, whom you can see dozing here:

Rainer looks so chubby and content; I love it. Cody, his adopter, said that Rainer has been great with the puppy. I asked him how Rainer was doing in general, and his sole comment was: “He has been a real blessing.”
I’ll take it! I’m always amazed at how much our former foster dogs have grown and matured since we had them in our home. Rainer was perhaps our hardest case, and I can’t say how much joy it brings me to hear that he is doing well — and coexisting peacefully with a sibling.
Have you ever been surprised by a dog’s behavioral change, particularly once he or she was in a new environment?