I was out walking Thor today and we met up with a woman who had a female 3 year old GSD. Thor sat when he saw the dog, then as the dog came toward us (the dog was barking excitedly), she put her head over Thor's head and then Thor expressed his glands and started barking back at the female dog. Thor was not barking aggressively or defensively at the dog, he just seemed excited. I have never had a dog express his glands like this, any thoughts why this behavior occured? Dominance, excitement? We have a female dog at home who Thor is with all of the time and this hasn't happened when they are playing?