An anecdote from my school days. I was 15 years old and turning a piece of brass for the cylinder on the steam engine I was building for my final year exam.
Let's call this lad Brian... Brian was a cunt, and he was working on the lathe beside me. I looked across and saw him closely examining the job he was working on, whilst the lathe was running. After a double take, it transpired that he wasn't closely examining it, he was slowly getting dragged into the lathe by the tie around his neck, which he'd left dangling outside his school jumper, and it had got wrapped around the lead screw, dragging him into the lathe. I immediately realised what was happening, and hit the emergency stop on his machine, and when I asked him why he hadn't pressed the E-stop himself, or cried out for help, he told me that it was because he was in shock and didn't know what to do.
I guess the moral of this story is this... Let Brian sort his own shit out. He turned out to be a racist cunt, and it would have been better if you'd let the lathe take its course.