http://www.youtube.com/watch?v=TPJ65araum4

its called piper.

I see some people associated with it, act like it's this big secret unique art, but people have been using this sort od stuff open handed for years in a variety of things, magicians, slap fighting, tickling your kid brother, etc

Information about it, below link.

http://themanwhonevermissed.blogspot.com/2010/01/piper-knife.html

Regards,
Gary