During a proficiency check of a qualified pilot, the instructor closed the throttle at the start of an autorotation and opened it at about 50 ft to prepare the aircraft for the power recovery. However, the qualified pilot did not attempt to the flare the helicopter, even when verbally prompted by the instructor. To assist the pilot, the instructor attempted to flare but found that the pilot had “frozen” on the controls to the extent that the instructor was unable to override the pilot. Consequently, the helicopter hit the ground with a nose-down attitude before coming to a rest on its left side. Both pilots, who were wearing lap and diagonal harnesses, suffered minor injuries but were able to exit the helicopter via the right-hand door.