I used to have a butterfly knife 20 years ago, great fun (even though illegal in Canada). I miss flipping it open and closed, decided to try to find one of the bottle opener ones I recently saw, found this one on a site in Quebec, bought it, looking forward to legal fun.
Check out the video they have posted, good fun to watch the guy, his mistake, then his joy at performing the techniques flawlessly.
http://www.letigreargente.com/butterfly-knives.html