Helicopter blade sailing.....
There are numerous recorded instances of the helicopter blades chopping off the tail, smashing into the cockpit roof (see
http://www.pprune.org/rotorheads/455...astonbury.html post 4 for a picture) and there is a Youtube video of a US military CH-53 helicopter chopping off the refuling probe with his rotor after a little "rough handling"
You may not have to duck when moving under a helicopter rotor, but each person can only make a wrong call once.