On December 1, 2015, about 1530 eastern standard time, a Robinson R22, N8560M, made a forced landing to a field near Venice, Florida. The flight instructor sustained minor injuries and the private pilot was seriously injured. The helicopter was registered to N8560M, LLC, and operated by Helicopter Academy under the provisions of 14 Code of Federal Regulations Part 91 as an instructional flight. Visual meteorological conditions existed near the accident site at the time of the accident and no flight plan was filed. The flight originated from the Venice Municipal Airport (VNC), Venice, Florida, about 1430.The flight instructor reported that he was preparing the pilot for her commercial rotorcraft-helicopter checkride. They had practiced several maneuvers before heading back to the airport. While en route to the airport, the instructor was asking the pilot where she would land in the event of an engine failure when he noticed that the manifold pressure had dropped below 18 inches of mercury, which necessitated activation of the carburetor heat. The instructor did not recall if he told the pilot to turn the carburetor heat on, but remembered looking back outside because they were discussing forced landing areas. The instructor said the pilot then accidentally "pulled the mixture" versus the carburetor heat and "shut off the engine." He immediately took control of the helicopter, entered an autorotation, and landed "hard." The windshield popped out and the helicopter rocked back and forth before it came to rest. The instructor said the pilot then exited the helicopter and ran toward the front. The main rotor blades were still moving and struck the pilot's head. The instructor said he never saw the pilot actually pull the mixture control in flight. He assumed that she did, because when he went to shut the engine down, the mixture control's safety gate was on the floor and the mixture control was pulled out. The pilot stated that while returning to Venice, the instructor asked her where she would land if they had an engine failure. She said the beach, but the instructor pointed out a more suitable spot. The instructor then called out "3-2-1" and rolled off the throttle to simulate an engine failure. The pilot said that both of them were on the controls and the autorotation looked good until they were about 250 feet from the landing spot. The helicopter landed hard, but she did not know why. Once on the ground, the pilot said she "pulled the mixture" while the instructor had his hand on the rotor-brake. She then exited the helicopter to go retrieve the windshield that had popped off during landing. While standing out in front of the helicopter, one of the main rotor blades struck her on the left side of the head, fracturing her orbital bone. Both the instructor and pilot reported there were no mechanical deficiencies that would have precluded normal operation of the helicopter or engine. The instructor held a commercial pilot certificate for rotorcraft-helicopter and was also a certified flight instructor in rotorcraft-helicopter. He reported a total flight experience of 700 hours, of which, 600 hours were in the R22. The instructor's last Federal Aviation Administration (FAA) second class medical was issued on August 11, 2015. The pilot held a private pilot certificate for rotorcraft-helicopter. She reported a total flight experience of 150 hours, of which, 150 hours were in the R22. The pilot's last FAA second class medical was issued on June 6, 2015. Weather reported at VNC at 1535 was wind 310 degrees at 6 knots, clear skies, and visibility great than 10 miles. The temperature was 79 degrees F and the dewpoint was 72 degrees F.