I've stuck many a finger in a case/HS fan, never did any serious damage although it hurt like hell when a fan blade whacked off a burn blister from a stove incident.
Have a funny electrical story though...Working Customer Service at a grocery store when I was younger. Some guy return a disposible camera because it didn't work. Being that working as a grocery store is boring as hell, I got bored, grabbed a screwdriver out of the junk drawer, and began prying the disposible camera apart. Apparently, I forgot all the electrical stuff I'd learned, and no sooner had I jammed the screwdriver into the body of the camera, than I got a nasty jolt and threw/ejected the screwdriver about 20 feet away. As it turns out, even though it only had two AA batteries installed, it also had a flash. And where there's a flash, there's a big-ass capacitor, which I'd managed to touch both leads of, discharging the cap into myself.
...But in some strange way, it felt kinda good...Except for the little invisible (yet painful) burnmark the screw in the screwdriver handle left in my hand...