According to a book I was reading about brains in general, the dog's brain cannot project forward (no great surprise) therefore dog is in a state of perpetual 'presentness'. When the pack go out, leaving the lone dog, they think (or as far as we know) — that's it . . . I've been left for ever. That's why they are so pleased to see you on your return, not because you are the best thing since marrow bone.
More ear soon.