Foreigner learning English from the radio Joke

Lawl, I read this little joke in the book Quantum Psychology (highly recommended btw):


Thus in a famous Sufi story, Mullah Nasrudin, wisest man in Islam, entered England on a visit. "Do you have anything to declare?" asked the customs inspector.
"No - ssssssst, bzzz - nothing at all."
"How long do you plan to stay?"
"Oh about, sssszzzzzt, bzzzz, - about 3 weeks. "
"By the way, where did you learn English?"
"From the - bzzz, bzzzzz , sssssszzzzz - radio."

i always wondered why i dont hear many jokes from quantum psychologists.
thanks for clearing that up.