Part 981 and Part 982 are curved pieces that represent a minifigure's arms. The arms connect to the torso and hands to create the "middle part". When opened, a set comes with the arm and hand placed onto the torso already. These extra pieces do not affect the piece count. The part number itself, 981982 comes from the fact that the left arm is Part 981 and the right arm is Part 982, so they are thought of as Part 981982, which is matching left and right arm.