For about a week or so now, the pup's been barking at things going on outside the front of the house - people standing and chatting, and dogs walking past. He cannot see these things from where he is, he just woofs at them. Compared to his usual bark, this is a much deeper, more abrupt "ruff, ruff" kind of sound. He's mainly prone to doing this in the evening, which is when he's also the most hyper (despite being walked, trained and entertained during the day). If he's tired he's fine. Today, when I was training him on the front driveway (I was training him to pay more attention to me outside the front of the house), a Labrador walked past the far end of the driveway. The pup barked really loudly, then growled at it . It was really out of character for him - typically, he's really pleased to meet dogs (and still wants to jump on their heads ). It was midday, the pup was sleepy rather than hyper, and the Lab wasn't doing anything other than just walking past. Until now, my dog has rarely growled- except for play growling during tug-of-war. He has never growled at a person. He's only ever once growled at a dog, and it was during his puppy classes when a (different) Labrador tried to bounce on him. (He has met Lab's before and since then and has been fine with them. Except for today's Lab. But I'm not sure it's possible for a dog to be breed-prejudice). I can't work out if he's becoming territorial, growing up, or just developing some bad habits?