In the last scene, Doug is sitting at a hockey game listening to the national anthem of Canada being played, as the visiting team is from Canada. As he comes to the realization that he is Canadian (as his mother disclosed that he was born in Montreal), he stands up. In actuality, everyone should have been standing for the Canadian national anthem as it is custom to stand for the national anthem of the visiting team, which is played first, then the home team.
When Doug first confronts his parents in their living room, about his "immortal" dog, Rocky, a boom mic can be seen in the reflection of the sliding glass door behind Doug and his mom. When Doug starts to walk around the couch, the boom mic can be seen following his movements in the same reflection.