the index finger used to prevent sneezing (aka sternutation) by placement under the nostrils, above the top lip of the mouth. Most famously seen in Dopey, of the Seven Dwarfs. Also used by the Jupiter Group at Westerlin in their attempts to reach Jupiter by the year 3000.
I was about to sneeze all over "Slightly Off Center: Selected Works of Otto Von Grieg," when I remembered the Grieg Finger, and all was saved. I got the nostril thrill!