A real gravity knife is like this:
Thanks for posting the video. I had heard the term before, but never really understood what that meant and how it would actually work.
Up here in Canada, certain types of knives are verboten ... auto knives main among them. (And balisong, gravity knive, &c.) Not being able to get one, part of me now wants one just to have one. On the other hand, having been "forced" to look to other options, I have found other options for one-hand-opening knives that work just as well for me ... and probably have a stronger locking mechanism than the forbidden knives.