Material Link

A material link is something that is an integral part of the target. If the target is an inanimate object, the link has to be something that is an essential part of the object’s structure. A brick from a wall could be a material link; a picture hanging on the wall or other loose object from inside the building could not. If the target is a living being, it must be a tissue sample. Tissue samples, however, decompose eventually and cease to become viable as a material link. Hair, blood and other bodily fluids, nail clippings, and so on are viable for a few hours, while a finger or larger tissue samples (such as the proverbial pound of flesh) can last a few days before the being’s aura fades too much for it to be a link. Chemical preservation methods instantly destroy the sample’s viability as a material link, but samples can be frozen for later use.

(CRB 297)