In Baldwin v. Knight (Tenn. 1978) 569 S.W.2d 450, the alleged negligent act was a doctor's failure to determine that a patient's puncture wound following a lawnmower accident was caused by a flying object (a wire) that had become lodged in the patient's leg before closing the wound. (Id. at pp. 451, 456.) The Supreme Court of Tennessee concluded that this subject was within the common knowledge of a layperson. (Id. at p. 456.)