Why do dogs sniff each other butt?

It will happen to you, at least once in your life, to leave the house with your dog, or at least walk down the street or to the park and see two dogs who meet and, the first thing they do is sniff their butt each other, and you smiling for the funny situation, have you wondered why; the answer is very simple: for dogs, the smell of the seating is more useful and informative. In fact, for dogs the smell, among all 5 senses, it is the most important; being the butt one of the parts of the body that gives off more odor, it can provide a lot of information through pheromones, ie those chemicals that change depending on the social, emotional and sexual dog (but also of the people).
One can therefore say that when a dog sniffs an another  butt , is asking implicitly as it is all ok, and, therefore, let sniff it means to talk about himself; the same way the dog also needs to sniff people to understand who you are, and, thanks to our pheromones, is able to perceive when we are afraid or dangerous, that’s why it can be happened to have heard it said ‘do not be afraid, the dog feel it’.