I remember years ago before the first Spiderman movie came out one of the cereal companies had a thing where you mail in a a certain number of UPCs and get a cd with a demo of a terrible spiderman game and a bunch of wallpapers and screensavers. The one that really freaked me out was an interactive screensaver that was just an image of a web across the center of your screen that would blow in a gentle breeze. And whenever your cursor brushed the web it would stick slightly, and if you didn't move fast enough or hit the web too hard your cursor would get stuck. At which point this quiet chittering noise would start, and the gigantic, hairy, spider-thing would slowly crawl out onto the web and pounce on your cursor to devour it. At which point numbers would begin trailing across the screen and parts of the screen would begin to flicker and die, building until there was a flash and the whole screen blanked out for a few seconds.
The first time I did it I thought I had killed the computer and was scarred for life.