I thought it was you, Charles, but I guess it must have been someone else. I'm sorry. It was told in an thread explaining why we use iaito in Iaido.
Anyway, the story goes like this. Our nameless swordsman (who is apparently not Charles Mahan) was practicing Iaido in class. The move he was making required the saya to be angled close to the horizonal, but he missed that part and had it close to vertical. As he drew from this incorrect position, the move became impossible. The iaito slipped out of his control and jammed into his left arm. His arm was heavily bruised, and his sensei said that if he had been using a sharpened blade, he would have cut his hand off.
Fencing Club at UH