If you want to be an assassin but you're not sure where to begin, this Youtube video explaining how to build your very own Assassin's Creed hidden wrist blade with parts you can pick up at your local Home Depot might be just what you're looking for.
Let me begin by saying that I'm not in any way recommending that you try this project and if you do, and you manage to put it all together without slicing your fingers off or poking an eye out, for God's sake don't go outside with it. You will get arrested, and there's a pretty good chance you'll get preemptively punched out by some do-gooder citizen who decides to take you down before you can kill someone, too.
That said, this home-made hidden dagger is one seriously cool piece of work. What makes it so impressive is that despite the simplicity of the design, the blade both auto-locks and auto-retracts: You don't need to hold it in place once it's popped and it'll instantly snap back when the job is done. Yet the whole thing is built out of just a small spring, a paperclip, some string and a 14-inch drawer slide cut to size with a Dremel.
It's simple to make, easy to conceal and, let us not forget, dangerous and against the law in just about every corner of the civilized world. Even the builder, who goes by the name of TheBserk, acknowledged that this weapon is illegal anywhere outside of his house. That said, Halloween is coming and this is one mighty cool assassin accessory - but rather than that finely-honed seven-inch blade, you might want to think about using a comb instead.