TL*THE CONTACT OWNS A 2007 TOYOTA PRIUS. THE CONTACT'S SPOUSE WAS BACKING DOWN A 20 DEGREE SLOPE WITH HER FOOT ON THE BRAKE PEDAL. THE VEHICLE ACCELERATED BACKWARDS DOWNHILL AT APPROXIMATELY 5 MPH, BUT THEN ACCELERATED TO 35 MPH. THE CONTACT CONTINUED TO DEPRESS THE BRAKE PEDAL. THE VEHICLE STRUCK A TREE AND THE CONTACT'S HEAD STRUCK THE HEAD REST. HE SUSTAINED A HEAD INJURY AND CAN PROVIDE A POLICE REPORT. THE DEALER WAS NOTIFIED AND THE VEHICLE WAS REPAIRED. THE CURRENT MILEAGE WAS 12,700 AND FAILURE MILEAGE WAS 10,600.