Well, it could stem from the fact that I once was riding along, letting my shoe rub against the front tire...it made a cool sound! Suddenly, that foot and that bike tire became all too acquainted with each other. With my shoe squarely against the tire, my foot slid up against the front fork and stopped the front tire. But the rest of the bike was still moving! I "endoed" and landed on the pavement. It didn't cause any lasting injuries, but I haven't really tried it since.