A large Scimitar, from times of yore, that would easily knock off an enemy's head with a single swipe. Show it clearly on both sides. Run it along your bare arm, then with a twist, slice it right in. It goes through, right to the bone. Let them see it from all sides. it really goes half way through the arm. Then pull it out, and there's just a large red welt where it sliced through your hand, no blood, no gore . Wait a few seconds, then wipe away the welt, and there's no trace of the cut.

The effet is done with the single Scimitar, which the audience can clearly see at all times. No covers, no handkerchiefs, no exchanges.