I heard a more imaginative torture, from someone who grew up around cattle.
Apparently a calf will try to suckle anything that looks like a teat.
Tie the guy face-out around a tree, or spread-eagle to the side of a barn, or something like that, put a little milk on the little thing, and show a hungry calf. Adding a tube taped to his belly that would dribble milk into the area would encourage the calf.
It also helps the vision of a properly dealt-with rapist if you know that, to encourage a cow to let down her milk, the calves butt her with their heads. Imagine that solid little skull hitting the rapist's tender bits...
Brings a smile to my face.
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Then there's the one suggested by someone who thinks much darker thoughts than I:
Get a small-diameter glass tube or rod, like is used in a chemistry lab.
Insert it.
Clap it between 2 bricks.
All the men reading that just winced & tried to curl up.
The real reason women aren't allowed in military "combat positions" is because we're too bloody-minded.
Men fight fair; women don't.