A blonde named Pam is appearing on
"Who Wants To Be A Millionaire"  with Regis Phil. 
Regis: "Pam, you're up to $500,000 with one lifeline left: phone a  friend. If you get it right, the next question is worth one million  dollars. If you get it wrong, you drop back to $32,000. Are you ready?"
Pam: "Yes."
  Regis: "Which of the following birds does not build its own nest? Is it  A) robin, B) sparrow, C) cuckoo, or D) thrush."
  Pam: "I'd like to phone a friend. I'd like to call Carol." 
Carol (also a blonde) answers the phone: "Hello?"
  Regis: "Hello Carol, it's Regis Phil from Who Wants to be a  Millionaire. I have your friend Pam here who needs your help to answer  the one million dollar question. The next voice you hear will be  Pam's..."
  Pam: "Carol, which of the following birds does not build it's own  nest?  Is it A) robin, B) sparrow, C) cuckoo, or D) thrush."
  Carol: "Oh, Pam. That's simple. It's a cuckoo."
  Pam: "Are you sure?"
Carol: "I'm sure."
  Regis: "Pam, you heard Carol. Do you keep the $500,000 or play for the million?" 
Pam: "I want to play; I'll go with C) cuckoo."
  Regis: "Is that your final answer?"
  Pam: "Yes."
  Regis: "Are you confident?"
  Pam: "Yes; I think Carol's pretty smart."
  Regis: "You said C) cuckoo, and you're right! Congratulations, you >have just won one million dollars!"

To celebrate, Pam flies Carol to New York.
That night they go out on the town.
As they're celebrating, Pam looks at Carol and asks her,
"Tell me, how did you know
That it was the cuckoo that does not build  its own nest?"
 
"That's easy, everybody knows they live in clocks."