I'm a huge fan of horror cinema, and always have been, so for me, getting terrified is half the fun. Anyway, regarding what you said about observing other audiences, normally I'm too absorbed in the film to do this, but I do get a sadistic thrill out of seeing others jump out of their skin at particular scares. There's a particular jump at the climax of Wait Until Dark which had my wife and eldest son leaping off the sofa when I watched it with them recently. So funny.

On another occasion a few years ago, when frequently a cinema re-release of Jaws, I insisted on sitting between two people I had taken along (who had never seen it), because I wanted to experience their reaction to the greatest jump scare of all time (the notorious head in the boat) in stereo, so to speak. Immensely entertaining.