Two. One to change the bulb, and one to write a song about how good the old light bulb was.
or
Superman can fly, but a fly cannot superman!
or
Woke up in the fireplace.
or
"Let me see your birth certificate".
or
2 years old.
Cow: "Mooooove over"
Sheep: "Naaaaaaa."
or
It's not a shrub, it's a lemon tree my dear Watson.
or