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 there's no one else to wag it for him.
or
A stick.
or
Between you and me, something smells.
or
Chips AHOY!!
or
In Washington, D.C.
or