Guilt-casters were a specialized type of Bene Gesserit member of the Sisterhood who would bombard their ordered and intended victims with waves and pulses of psychic energy, while telling them of great guilt or disappointment they had caused the organization.
The most infamous guilt-caster employed by the Sisterhood was one named Stokia, who was used by the women to disable and render harmless Tessia Vernius of Ix. Other intended victims of guilt-casting were Lady and Duchess Jessica Atreides, when she visited Wallach IX; and Lady Margot Fenring exiled on Salusa Secundus. With Duchess Jessica, the Lady herself was able to beat off Stokia's attacks, with advice given by Tessia herself. Margot Fenring was able to beat back her assailant as Count Hasimir Fenring stabbed Stokia deeply in the back, as she attempted to render his wife comastose.