During the early days of my apprenticeship the machineshop foreman would go around and wack everyone on the head even if you left the chuck key in for just one second!
He had a fantastic sense of being able to be there just when you made any mistake whatsoever!
Sort of spot things like that from a mile away since then.
Guess it worked!
(he always had a real story for every mistake, from chuck keys, through cleaning swarf on a mill, to long hair pulling the operator's head into the machinery! - It was the 70's)