I work on an assembly line. The first person creates the torso of a doll. I then get the torso's and I pop a head onto the doll. The next person down the line puts the arms and legs on the doll. And finally, the last person dresses the doll. My bonus is an individual reward, based on how many doll heads I put onto the dolls.

What is wrong with this reward system and what might be a better option?