I've done that, held onto the key long enough to burn an impression of the key head into my palm. Thing is my older brother also stuck a key in a socket but he was weak and let go. Yeah my Mom did try to make sure I couldn't get a key after my brothers episode but I was an explorer and 2 year olds can vanish real quick when they want to.
I've always been enamored of mechanical/electrical stuff. When I was about 9-10 walking home from school (also did that in 2 feet of snow, around 1949) I spotted a thing in the grass with coils of copper wire, contacts, and other bits mounted on a black metal plate,. I picked it up and when I got home immediately retrieved my little bag of tools and set about trying to take it apart. Got a couple of wires loose and held them to a 6v lantern battery.
Nothing.
Noticed the wall socket.
Can you see this coming?
Stuck those 2 wires into the socket while holding the "thing"
in my other hand not really comprehending what was about to happen.
At once:
Wires went red.
Really loud buzzing.
Ice picks being stabbed into hand.
Lights started flickering.
Hand seemed to be burning.
"Thing" ejects from my hand simultaneously with lightning bolt shooting through my arm.
Flashbulb fired off behind my eye - don't know which one.
Not knowing any appropriate cuss words the best I could come up with was the loudest ouch I have ever uttered.
Mom runs into the room and I am unable to form the words to explain what happened...all of this transpired at the speed of light - I know because I literally saw the light.
I apologize for this non-S&W post but the key thing resurrected a memory that doesn't surface all that often and when it does I realize that I'm lucky not to have been killed...
I later came to realize that the "thing" was a voltage regulator that controlled the voltage output of the generator all cars had in those days.