Classic ?scary? magic using a volunteer (victim) from the audience. After inviting spectator up from the audience, have them examine your sword. You can talk about the ?rites of passage? for audience members ... they have to prove their worth through an act of courage and sacrifice. As you do, show the spectator the sword you have. After its been verified, show them the ?protective gear? (i.e. a neck shackle) that you will place around their neck. Lock it in place.
Now take the sword and proceed to PUSH IT completely through their neck, beginning at the base of their neck ... entire audience will be able to see you visually push the sword right through this person?s neck!

Of course, after you remove the sword and neck brace, your assistant is no worse for the wear!

Easy, but stunningly visual magic!