I was working with soil next to the horses and saw them scratching each other. No stalking required. For horses that is a typical way of showing mutual trust and friendship. Especially in the spring time, the thick winter fur gets loose and I guess it might feel itchy, so the horses like being scratched.

If a human scratches a horse, the horse often wants to scratch in return - they do it very gently with their lips. Sometimes it happes that I stand scratching one of my horses, and then the other joins us, and soon we have shared scratching. Feels like home =)