EE was attempting to nail two 2x4 boards together in a right angle. EE had a smaller 2x4 standing on end with the longer 2x4 on top. Was holding them together with left hand. Brought the automatic nailer up and then back down on the top of the board. EE missed the center. The nail grazed the edge of the board, deflected and penetrated EE's hand. A doctor removed it.