Mount And Blade Legal Serial How Could I Make A Spring-loaded, Wrist Mounted Blade? Any Legal Risks?

How could I make a spring-loaded, wrist mounted blade? Any legal risks? - mount and blade legal serial

Well .. I want to do something .. So I thought to do real work rather well, and just awesome .. Im not sure if you've played Assassin's Creed, but that's where I got the idea.

http://assassinscreed.wikia.com/wiki/Hid ...

I have not cut my fingers, I do not intend to kill anyone .. (I thought bout Going Ape in a Watermellon with it just for show ..

But .. How can I do? It always fascinates me .. How, how could cause the fire and how quickly he could be, and I am able to swivel around and stab even somthing like a melon ..

One more thing .. Is there a legal risk?