When a horse blows into the other horse's nostrils it is saying 'hi' and when the other horse blows back he or she is returning the greeting. You can also say 'hi' to a horse by doing the same thing: get a little-just a little- to the side of the horse, take in a deep breath and blow directly into the horse's nostrils, if the horse blows back he is saying 'hi', if the horse dosn't blow back keep blowing until it does, it takes awile for a horse to get used to a human saying hi. I did this once to a horse that didn't even know me. It took about five trys before she blew back. After I say with my oun eyes it worked i told my friend to do it. It took her about five times two. When I got home I was so exited. I LOVE horses!