I have a confession to make. As a ski bum in Alta, Ut after college we had to ski a high traverse that followed a ridge line and was marked for expert skiers only. It never failed that somebody would be there doing a snowplow. if I called out "on your left" people would look aver their left shoulder and unconsciously weight their right ski. What happens when you weight your right ski? You turn left! The traverse was only 7-8 feet wide in most places so it almost always forced you downhill to miss the collision. Some where along the line I called out "On your left" and waited for the left turn. Sure enough it happened over and over again. I was better off not saying anything or when I did say "On your left" then slip sideways, wait for the left turn, then shoot the gap and pass on the right. Really entertaining when your 24 years old.