The law of contagion is a folk belief that suggests that once two people or objects have been in contact, a magical link persists between them unless or until a formal cleansing, consecration, exorcism, or other act of banishing breaks the non-material bond.
Psychics and mediums commonly utilize an object once owned by a missing or deceased subject as their "focus" for psychometry or clairvoyance or during séances.
Dangers include, for example, a sorcerer or witch might acquire a lock of hair, nail clipping or scrap of clothing in order to facilitate a curse.
In cultures that practice sorcery individuals often exercise care that their hair or nails do not end up in the hands of sorcerers.
Even among people who do not profess a belief in magic, psychological experiments have shown a reluctance on the part of the public to, say, try on a sweater worn by a serial murderer.