It's actually pretty similar to the story of Achilles. Everyone knows about how when Achilles' mother dipped him into the river Styx, making him invulnerable, she held him by his heel, thus leaving his heel exposed to injury. Bophades is similar - but instead of holding him by his heel, his mother held him by his testicles. So while most everyone is familiar with the story of Achilles' heel, very few people know about Bophades nuts