The three most terrifying things in the world are werewolves, clowns and unplanned pregnancy. Humanity has known this since time began and as such has endeavored to make sure the last one of these would happen as infrequently as possible.
When you combined extreme motivation, human ingenuity and the fact that most people are stupid, you wound up with contraception methods that will blow your mind. Or at least leave you feeling a little weird down there.
In the Dark Ages in Europe, things were dark for a reason, not the least of which was that, with the lights on, a typical man might wonder why his girlfriend had weasel balls strapped to her leg.
The reason is obvious to anyone with a degree in Magickery or Weasel Ballogy, as any magician at the time would tell you that the weasel balls would prevent pregnancy. Through the power of magick, you see. Yes, being a magician during the Dark Ages pretty much gave you a blank check.
We may not be magicians and our amateur dabbling in gynecology has been less than revealing, but we're pretty sure this method is aces since we don't know many men who would be able to perform sexually after seeing a pair of innocent, severed balls hanging from his mate as decoration.