I have tried this on my college's campus from time to time. I have come to one conclusion: no matter where you are walking, 85% of the people around you find the ground completely engrossing. The general aversion to eye contact amazes me. Not only that, but this campus has some fantastic architecture. Of course, the key to seeing this is to look up.
To confirm domaindudu's writeup, it is exhillarating to successfully execute this maneuver. And no, it does not matter if conversation comes about. It's almost more fun just imagining what might be said by this intriguing person, whose eyes you have engaged in a staring match.