Near miss- old Tcart, 65 hp. Pulling thru to prime, pilot at seat, old blade switch mags OFF. Motor started second blade pulling through.
No danger up to this point. Motor idling, pilot animatedly motioning that switch blade is "OFF", come see it. Felt like a mile walking around the prop arc to go see it was off still.
He swiped it to both and asked if we could check it before he flew off. I said I was done propping for the day. His mag check was normal, no idea if "off" worked later.
Before asking or propping, know how the ignition is wired and how priming is best done. Impulse coupled mags only, breaker retard/slickstarts need some minimum voltage as does EI.