The scariest piece of human engineering I'd ever encountered was when I took a few months in a cabinet shop for a friend.
Lemme see if I can describe this hellish monstrosity. I still shiver from the thoughts of what could have been.
A 10" toothed blade without a guard at the end of an arm which was purpose built as a cut off saw for rapid cutting of multiple like sized pieces such as the stiles for cabinets. The arm extended to a hub which held a belt driven gear
which powered the blade along a drive shaft which was the length of the arm. Continuing outward the opposite side of the hub was a counterweight. So...the open (unguarded) saw blade was on a swing which was exactly matched by the counterweight which meant the saw blade was so statically balanced that this spinning wheel
of death could swing near endlessly. The only thing holding it in check was your hand upon the handle soldered to the head
of the arbor which held the saw blade. That plus the ON/OFF switch. Of course, it would take milliseconds for that thing to spin up (torque!) but a few seconds to come to a stop when switched OFF. Meanwhile, if you ever let go of the arbor head, she would swing freely and it was a guessing game
if you could again attach your hand correctly and timely to the handle.
Even with the saw switched OFF it would swing about it's supporting axis. The saw of death. At least a router or shaper bit might take only the flesh from a finger. And a table saw or band saw might only take the stray finger or web of hand. But this thing I describe would take a whole hand or arm or conduct open heart surgery if allowed.