I am not a lawyer so it would be perhaps better for me to keep my mouth shut, but obviously I can not. <img src="/images/graemlins/wink.gif" alt="" /> So at least take this with a grain of salt.

In terms of physics it is not the centrifugal force that opens the knife but angular momentum. Centrifugal force is present only during rotation of the wrist while the knife flicks open after (and because of) the wrist comes to an abrupt stop.