Slave girls, when being transported in sacks
Slave girls, when being transported in sacks, for example, on wagons or on the shoulders of men, are usually completely within the sack, it being tied shut over their head. This helps keep the girl in ignorance as to her whereabouts and what is going on about her. This is thought suitable for slaves. She is also, after having been in a sack for a time, likely to be extremely grateful to he who releases her and very fearful that he might, if displeased with her, return her to it.
Blood Brothers of Gor, p. 642