Three:
One to write the light bulb removal program,
one to write the light bulb insertion program, and
one to act as a light bulb administrator to make sure nobody else tries to change the light bulb at the same time.
or
Because he saw the salad dressing!
or
It's not a shrub, it's a lemon tree my dear Watson.
or
They screw millions of bulbs every day, but when it comes to your bulbs, there's no record.
or
Two babies screaming!
or
The strange charm of a top down bottoms up.
or