The ducking stool was a punishment that most often befell women prisoners. Grossly unpleasant and often fatal, the woman would be strapped to a seat which hung from the end of a free-moving arm. The seat and the woman would be dunked into the local river or pond. "It was up to the operators of the stool as to how long she remained in the water." Many elderly women were killed by the shock of the cold water.
One 'foolproof' way to establish whether a suspected witch was a witch was by ducking. With right thumb bound to left toe, the accused was plunged into a convenient pond. If he or she floated, it proved an association with the black arts, with the body rejecting the baptismal water. If the victim drowned, they were innocent. Given the curious position of the prisoner, it was more likely they would float.