 Anal dildos and butt plugs generally have a large base to avoid accidental complete insertion into the rectum, which may require medical removal.Some women use double-ended dildos, with different-sized shafts pointing in the same direction, for simultaneous vaginal and anal penetration, or for two partners to share a single dildo.In the latter case, the dildo acts as a sort of "see-saw," where each partner takes an end and receives stimulation.