But that's the bit I don't get in that scene (at least in the Russian dub I've watched) -- the historical dunking test was that the suspect was guilty if she survived dunking, hence would be burned, but innocent if she drowned (sadly dead, but at least her immortal soul was saved). So what precisely does the dunking test show if you give them respirators? They all survive, so they're all guilty?
I believe the test was that if she floated, that is, if water, the baptismal element, rejected her, then she was guilty. If she sank, that meant that water accepted her, and she was therefore innocent. Suspected witches would have a rope tied around them so they could be pulled out of the water, but as I understand, drowning was a danger; regrettable, but as you say, at least the immortal soul was innocent of being in league with the devil. Interestingly, the Germans had it the other way around. If you floated you were innocent. I think this is yet another indication of German efficiency: If she sinks, fuck her.
They test the problem and solve it at one go.
An illustration by Bessonov (L). Note that the thumbs are tied to opposite toes, which is the right and proper way to prepare the accused, and (R) a suspect floating, and therefore failing the test. She is a witch! (At least in America and Britain.)
Dunking, or more commonly ducking, usually involved placing a woman (and it was considered primarily a woman's punishment) in a ducking chair or "cucking stool" and submerging her at intervals, the number of times depending on the severity of the crime. According to Wikipedia it was used on suspected witches but given that the purpose was to test the suspect's response to water, not specifically to drown her, I don't know how the ducking stool would work in that usage. Ducking was a punishment for scolds, disorderly women, prostitutes, women who'd had an illegitimate child, and other comparable crimes.
A ballad from 1615:
The Cucking Of The Scold
Then was the Scold herself,
In a wheelbarrow brought,
Stripped naked to the smock,
As in that case she ought:
Neats tongues about her neck
Were hung in open show;
And thus unto the cucking stool
This famous scold did go.[5]
en.wikipedia.org
It is disappointing that the scold is "stripped naked to the smock" which is not quite what we typically understand on this forum by being "stripped naked," but I suspect is what writers of those times meant by it, whether specifying the smock or not.
I agree with you: the way the ducking stool is used in the movie makes no sense, either as a test to determine if the woman is guilty of witchcraft, or as a social punishment.