In some forms of fictional magic, parts of a person are used as a medium of sorts.
Whether voodoo or tracking.
I suppose science can be similar in some ways.
Fingerprints can be used for tracking people, or allowing access through locked doors.
Some viruses and diseases, effect people of certain genetics more.
Dogs can track based on scrap of person or clothing.
People have talked about giving robots a sense of smell.
Knowing someone's true name,
Knowing someone's name and address,
Mailing them items.