King Arthur was in Merlin's laboratory where the great wizard was showing him his latest creation. It was a chastity belt, except it had a rather large hole in the most obvious place which made
it basically useless.
"This is no good, Merlin!" the King exclaimed, "Look at this
opening. How is this supposed to protect my lady, the Queen, when
I'm on a long quest?"
"Ah, sire, just observe," said Merlin. He then selected his most
worn out wand, one that he was going to discard anyway. He
inserted it in the gaping aperture of the chastity belt whereupon
a small guillotine blade came down and cut it neatly in two.
"Merlin, you are a genius!" said the grateful monarch. "Now I can
leave, knowing that my Queen is fully protected."
After putting Guinevere in the device, King Arthur then set out
upon a lengthy Quest.
Several years passed until he returned to Camelot. Immediately he
assembled all of his knights in the courtyard and had them drop
their trousers for an informal 'short arm' inspection.
Sure enough, each and every one of them was either amputated or
damaged in some way. All of them, except Sir Galahad.
"Sir Galahad," exclaimed King Arthur. "You are my one and only
true knight! Only you among all the nobles have been true to me.
What is it in my power to grant you? Name it and it is yours."
But, alas, Sir Galahad was speechless.