Ectophagia

Ectophagia is the practice of consuming a ghost for Essence or Plasm.

Ghosts in the upper parts of the Underworld routinely consume castoffs, Barghests and other non-human ghosts, if they have no other way to regain Essence. The Bound, too, can consume these ghosts for Plasm. The corpus of a ghost mimics the structure of the living equivalent, so the experience usually isn't pleasant: it exactly resembles chewing paper, wood, plastic, or raw meat. The ectophage gains 1 Plasm or Essence for every point of aggravated damage inflicted.

Consuming a humanoid ghost is, mechanically, no different than eating any other ghost, though the experience of eating a chunk of something that can struggle, scream and beg for mercy is traumatic enough to count as a Breaking Point for ghosts, and costs Sin-Eaters a dot of Synergy. This sort of cannibalism is also not uncommon in the Underworld, unfortunately, as desperate ghosts turn to desperate measures to avoid being absorbed into the Underworld.

A Sin-Eater who consumes a geist gains not only Plasm, but also learns that geist's innate Key. A geist currently bound to a Sin-Eater cannot be eaten. A geist can consume a Memento, completely destroying it, but absorbing all the stored Plasm inside in the process.

Ghost Eaters are mortal necromancers who have learned to ritually consume ghosts for Plasm.

References

GTSE: Geist: The Sin-Eaters Second Edition, p. 95, 99, 221