The Supplication of the Anakim was a summoning ritual that required that the supplicant cut their throat open with a piece of glass that had been baptised in four specific materials. The inhabitant's body would then turn into a vessel for other presences.
In 1762, Mary Culver used a broken piece of glass to slit her neck as part of the ritual. (PROSE: The Adventuress of Henrietta Street, AUDIO: Sabbath Dei) She became an avatar for Compassion, who used her to battle Lolita. (AUDIO: Sabbath Dei, In the Year of the Cat)
Sabbath Dei, who was investigating the ritual for the Service, used the same piece of glass to experiment with the ritual, which summoned the Great Houses; while he didn't let them take absolute control of him, (AUDIO: Sabbath Dei) they used him to arrest Cousin Justine of Faction Paradox. (AUDIO: In the Year of the Cat)