The "Make Your Own Voodoo Doll" kit read, "For the ultimate control over your subject, there's nothing like creating from scratch." The kit included an instruction manual and several small magical items such as an enchanted chicken feather, a quartz crystal, a small mortar and pestel, and a few items you didn't recognize. You wanted this and bought it.
You took it home and started reading the instructions. Of course you needed to get hair from the subject and attach it to the doll but the instructions said that the final effect depended on how you attached the hair. You were careful to attach the hair precisely as instructed. Because you followed the instructions so carefully, you are now able to control different body parts separately. For example, you can make the legs grow long and large while causing the arms to shrink. You can even completely remove body parts or move body parts to other places on the body. You are so glad you bought the kit because now you can really play with a certain person like your own personal toy.