Whether at the movie theatre, a live performance, or a sporting event, there are certain things that will always provoke extreme reactions in the audience, whether covering their eyes, plugging their ears, or curling into a fetal position. Here are the top five ways to ensure that your audience will squirm:

#1 Trauma to the groin.  This classic can run the gamut from America’s Funniest Home Videos baseball-to-the-crotch gags to Bill Pullman having his testicles punctured in The Serpent and the Rainbow, but rest assured that the audience (especially but not limited to the men) will be shifting in their seats.

#2 Injury to fingernails.  A personal phobia of mine, examples include Jeff Goldblum’s nails falling off in The Fly and the more subtle shot of the pit in Silence of the Lambs, where detached fingernails in its walls reveal not only the cruelty of Buffalo Bill but the futility of escaping his clutches.

#3 Teeth falling out.  Not being punched out or chipped, which is bad enough but manageable.  No, this is when someone gets a confused look on their face, feels around inside their mouth, and comes out with a tooth, root and all.  I happened to have seen two movies on consecutive nights which both included this very scenario: District 9 and Moon.  The fact that the tooth is naturally bloody doesn’t help.

#4 Hyperextension of joints.  This is most often seen in sports, in particular football.  A player is tackled, but his foot remains firmly planted on the ground, and the knee is pushed back in a direction it was never meant to go.  I was unlucky enough to see a rather brutal example of this at a Pirates game on Independence Day 1999, when Jason Kendall’s season was brought to an end after trying to beat out a throw to first.  It still haunts me.

#5 Sharp objects anywhere around the face.  It’s hard to narrow this down, because we’re all justifiably sensitive about our faces, and there are so many examples in cinema that are iconic: the razor blade to the eyeball in Un chien Andalou, the knife that Roman Polanski uses to cut Jack Nicholson’s nose in Chinatown, the razor (again) that exacts such fitting revenge against the Fascist commander in Pan’s Labyrinth.  If you’ve seen any of these movies, there’s a good chance that you closed your eyes and missed these scenes, and yet have a clear visceral image of them nonetheless.