The flight instructor reported that during the landing roll, the airplane began an "un-commanded" yaw to the right. The flight instructor further reported that the private pilot receiving instruction stated, "I can't control the yaw." The flight instructor reported that he applied rudder pressure to correct the yaw, but the airplane veered off the runway to the right, the left wing collided with an airport sign, and the nose gear collapsed. The flight instructor further reported that a jack rabbit was found in the runway excursion path and blood was observed on the left main landing gear door. According to a Federal Aviation Administration Aviation Safety Inspector who traveled to the site of the accident, the jack rabbit was not hit on the runway surface. The jack rabbit was found in the grass adjacent to the runway surface. The left wing was substantially damaged. The flight instructor and pilot receiving instruction did not report any mechanical malfunctions or failures with the airplane that would have precluded normal operation.