[LONG][STORY][NSFW] The King's Daughter's Guards

In a land that is far from here, but not so far from there, in an ancient time that is not so long ago, there lived a king.
Now, this king had a daughter, the most beautiful young woman in the entire world. As she grew to the age when suitors started appearing, the king grew paranoid that she would be whisked away by some secret lover in the dead of night, never to be seen again.
To stop this happening, the king stationed three guards outside her door every night to watch over her.
However, he began to grow suspicious of the guards themselves, thinking that they were sleeping with his darling girl. He was correct - every night, the guards would go in to the princess's chamber one by one, have crazy, vigourous sex with her and then leave to allow the next guard in.
The king came up with a failsafe plan to catch the guards. One night, he slipped his daughter a temporary sleeping pill at dinner and put her to bed, soundly asleep. As he was tucking her in, he placed ground glass shards inside and around her vagina, hidden from view. He then left, stationed the guards outside her door, and went to bed.
As soon as they were sure it was safe, the first guard went inside the room, and a few moments later the two guards outside heard an agonised scream from inside. The guard came stumbling out crutching his crotch. Too proud to admit what had happened, and not wanting to be the only one, he told the other two that he'd never had better sex, that it was absolutely incredible tonight.
The second guard rubbbed his hands in excitement and went in. The same thing happened. A few moments later, he let out a muffled, agonised scream and came running out of the room, also holding his crotch. As the first guard, he was too proud to admit what had happened, so he told the third guard (who by now was super excited) that she was feeling super freaky tonight and it was an incredible experience.
The third guard ran in, and the other two stayed outside, waiting for the scream, but there was nothing. Just absolute silence.

The next morning, the king called all three guards to his throne room. He asked the first guard to drop his pants. He did so, and his penis was covered with glass, blood, completely shredded. The king smiled, and ordered his head be cut off.
Then the king called up the second guard, and told him to drop his pants. The same thing happened - but worse. His penis was actually fully split down the middle, covered in shards of glass and blood. The king smiled, and ordered his head be cut off.
Finally, the king turned to the third guard, and told him to drop his pants. Fully expecting to see another mangled penis, the king was taken aback when he saw a perfectly intact specimen of a penis, gloriously free of blood and glass. Furiously, the king screamed "HOW DID YOU MANAGE THIS?! WHAT DID YOU DO!?"
The guard just looked mornfully at him, and replied "Mmmff mfffmmff mmfff..."