The good bit is that the dog whom we once seriously considered to have a case of mental arrested development seems to be showing signs of cognition -- he saw at the window another dog passing outside, and he wanted to get at this dog (in a friendly way), so he ran to the door. In other words, he has finally worked out the difference between outside and inside (which he didn't use to, judging from his toilet habits) and also connected that the door was what took you outside.
The bad bit is that he slammed against the closed door. Twice. Two thumps. And whined. He hasn't yet realised that it's only an *open* door that can take you outside.