I used to work in a machine shop that made heater manifolds.....well, at least that's what they were called lol. We would start with sheet metal and pipe and go thru to the finished product (basically a pipe with holes in it with a couple brackets welded on).
Anyhow, part of the process was to get the little 4" metal plates bent to 90 degrees. And we used some ancient HUGE press. You'd put the flat piece of metal on the form, press a button on either side of the press, and the big press part would come down and bend it pretty as you please.
Well, one day someone found a 'footswitch' that you could use on the press. You could just stand there with your foot on the footswitch and not have to press either of the buttons. I'm sure you know where this is going. The owner was not too happy when he had to clean up chopped off fingers not long after.........
Also, planars. The guys there would always say 'watch your ring as it might get caught on the blade and rip your finger off'....D: