when they get more advanced in their training they will cop an engine failure anywhere in that, at any height, but the ones who have got to the danger experience level of between 800 and 1200 hours and who have demonstrated a reckless disregard for the position of their tail close to the ground, definately will cop a full on T/R failure exercise at any time the aircraft airspeed reaches zero, but never from below 1500 AGL.
oh and don't have any loose articles laying around before you throw in the pedal, and don't for gods sake ever pull it on with a student until you are well practised in what will happen yourself.
if the victims are real smart arses then they will cop it first before we go through the routine t/r failure in the hover bit.