I don't think the picture is gross, as some have said. I don't think it's erotic either, but it sure is interesting. I wonder if her boobs are the "floppy empty sack" type when not being blasted by a full-frontal 120+ mile-per-hour headwind. Maybe firmer titties wouldn't cup like that.
Heh heh. You're intuition is correct. Note the woman on the left. Her left breast isn't inverted. Even firm ones have a tendency to cup, though. I came across another video showing the male's part doing some unusual things. I don't know if I should show it.