The video doesn't load for me. A similar article with video: <a href="https://news.ycombinator.com/item?id=5927510" rel="nofollow">https://news.ycombinator.com/item?id=5927510</a> (4 points, 5 hours ago, 3 comments)<p>Extract of comments: ... In case this is not a joke ... It happens only at daytime ... so it's probably dew to the vibrations caused by the public ... because the friction between stone and glass is small.<p>Note: An important detail is that it's not a "perfect circle", it's really only a half turn, so gravity is a possible explanation.<p>Another thread: <a href="https://news.ycombinator.com/item?id=5927620" rel="nofollow">https://news.ycombinator.com/item?id=5927620</a> (3 points, 4 ours ago, 4 comments)