Melt a small bit of chocolate (could probably even use the Reese's Pieces) in the microwave.
Using a toothpick, add a bit of chocolate to the back of a yellow Reese's Pieces and stick to the top of the Peanut Butter Cup. I was able to fit 4 on my snack size Peanut Butter Cup.
Add a bit of chocolate to the back of the candy eyes and place on the cup.
Break an orange Reese's Pieces in half and using a bit of chocolate, adhere it below the eyes.