“Waking a Witch”
If a “witch” was obdurate, the most effectual way of obtaining a confession was by what was termed “waking her.” For this purpose an iron bridle or hoop was bound across her face with four prongs thrust into her mouth. The “bridle” was fastened behind to the wall by a chain in such a manner that the victim was unable to lie down; and in this position she was kept sometimes for several days, while men were constantly by to keep her awake. In Scotland some of these bridles are still preserved.
Source: Dictionary of Phrase and Fable, E. Cobham Brewer, 1894