Sadly a bit of a horror story from me - many moons ago I was hand swinging a 100Hp Continental on a home build when the engine backfired (I believe that the impulse had stuck during suck ins & then released as the cylinder came up to compression), anyway it went backwards at 2000rpm leaving my thumb hanging from a thread
. Thankfully the wonderful surgeons at Odstock Hospital sewed it back on after a 2 hour wait (it was Christmas after all) & there it remains.
Not swung a prop since & shudder at the mere thought.