Nr decay Demo
One of the demonstrations that we used to give students on the RN Gazelle course was an Nr Decay Demo. We would get the student to put his hand on the roof-mounted throttle lever and then stare at the Nr guage.
From 90kts and on a countdown of three, we would get the student to chop the throttle and the instructor would say "F*** me, the engine's failed!" and then lower the collective fully. In that short time, the Nr would have reached the red-line minima, so a flare would be required to regain the Nr.
The instructor would then complete a perfect EOL to a specified spot!