Through the ancient art of voodoo, we discover the fundamental concept of referral, most notably, that of Indirect Referral - the idea that by affecting an inanimate object, we can simultaneously have an affect on a living recipient.
So what is required for this magic to work? First and foremost, something to tie the intended recipient to this inanimate representation. Often a Voodoo doll is infused with something related to its counterpart, be it a strand of hair, or it could be wrapped in a cloth that once belonged to its counterpart.
Next we have the pins. The pins, though bearing a clear negative connotation, at their essence, represent an action which is done to one, and the impact is then imparted on the counterpart.