A friend here took one of her dogs to another vet this morning, for a second opinion. The dog is about 15 years old, has some permanent medical issues, and appears to be living with pain. It has attacked both the friend and her other dog with no provocation multiple times recently, and seems like he just wants to be left alone.
Her regular vet has been treating this dog's lingering ailments for years, and wanted to keep treating them. The second opinion vet did an examination, and said that the dog had suffered too much already.
I've noticed that our dog has been acting sad this afternoon, as if he can sense that one of his friends is gone.....