"Ready for your daily blonde joke?" Astoria asks excitedly.
"No," Draco responds.
"That sucks. So, there's a blonde sitting next to a businessman for a really long train ride. The businessman decides to have a little fun with the blonde, by playing a mind game," Astoria adds sternly, after seeing the barely-concealed chortle Draco is suppressing.
"Sorry," Draco says, not sorry at all.
"The blonde just wants to go to sleep and so she finally agrees to play the game and the businessman explains the rules: if he asks a question and she can't answer it, she has to pay him five galleons. If she asks a question that he doesn't know the answer, he will pay her fifty galleons. So the businessman asks, 'What's the distance from the earth to the moon?' The blonde hands him five galleons.
"The blonde asks, 'What goes up a hill on three legs and comes down with four?' The businessman looks through nearly every book on the train and even starts owling friends and coworkers, but none of them know the answer. Finally, he wakes up the blonde and hands her fifty galleons. The blonde puts the money away, says 'thanks', and goes back to sleep.
"Frustrated, the business man wakes up the blonde and says, 'Well, what's the answer?'
"The blonde reaches into her bag, hands five galleons to the businessman and goes back to sleep."
Draco asks, "What was the answer to her riddle?"
"That's just the thing," Astoria says, "she didn't have an answer. Great way to make money, though. The businessman never said you had to have an answer."
"That's stupid," Draco remarks.
"You're stupid."