I have a newly-adopted dog for a little over 4 mos. now - good guess maybe 3-4 yrs old. He's a good dog, calm, has gone thru beginner and intermed training and even recently passed a temperment test to visit nursing homes. He'll bark at the door, but does not jump on guests and settles very quickly. He walks nicely on leash ... we pass and meet/greet lots of people and dogs. Once in a while he might get a little barky/jumpy with a certain type of dog (across the street), but has successfully met and politely greeted other dogs face-to-face. My problem is that - as I can remember - maybe three times since I had him, he's crossed in front of me on a walk to lunge at a passing PERSON. Each time it caught me completely off guard and puzzled me as to his intentions. Once was a young teenage boy, another was a gal ... both walking towards us and the dog crossed in front. I was able to catch the dog both of those times and correct him, all along wondering if he was being playful or going "after" them? Recently I took him for a walk and a friend joined us. Now, while there was nothing unusal looking about the first two people, I could see where my friend might cause him some suspicion, as he has a beard and wore a hat. My dog, had, however, met him earlier in the day inside the house without incident. When they were first meeting, I was especially alert to how the dog would react since my friend is a little out of the norm, appearance wise. As we walked, I had my dog on my right and my friend on my left. Casual walk, my friend and I talking, and dog was allowed to sniff here and there. Twice, however, my dog went from his normal walk to quickly cross in front of me and this time, was actually going to bite my friend! The first time I caught him, but the second attempt a few blocks later, my friend actually felt his nip on his hip. I was mortified! My friend was fine - no skin was broken or anything and he did not react in any dramatic manner, but I was just beside myself to now KNOW that this was my dog's intention each of the very few times he did this. Of course, I don't know doggie's background. Even being a calm dog, a lot of time was spent socializing in during his 6+ mos in foster care, but, of course, we have no idea what experiences he faced prior to that. I also understand that certain things can trigger a reaction from a dog ... hat, beard, etc. which my friend HAD, but the other two did not. In the past when we were approaching a "different" type of situation, such as a group of kids, or people on bikes, I would make him stop, sit, look at me and stay until they passed - then treat. I'm wondering what any of you might have to say about what the dog was reacting to. I've heard of on-leash frustration. Maybe it was protective behavior. But why would a dog who's walking along fine (especially in the case of my friend who was next to me rather than approaching) all of a sudden think to himself ... Oh! I better go bite that person!