Ugh. I can picture all of these scenarios all too well.
When I was a child and my younger brother was 4-yrs old, he left the dinner table, wandered into the living room and put the threaded needle of the treadle machine through his forefinger. Of course, we all rushed to see the cause of the yelling. My mother is still grossed out, thinking about having to turn the wheel to release his finger, then cut the threads.
Hopefully I learned by watching because I haven't duplicated his move.