I learned this gem of a close-up trick from "Lonnie Chevrie Live", a video lecture sold by Penguin.
It gets very strong reactions and is pretty easy to do. The re-set takes about a minute and cannot
normally be done in front of spectators (although Chevrie says he sometimes does it behind his back
while talking to people). The trick is so good that I have considered using it in walk-around,
even though I'd have to carry 4 little dental floss packs in my pocket to avoid the re-set issue.