A fence.
or
They charged one - and let the other one off.
or
Because it goes good with chips.
or
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
The letter G.
or
Aye, Aye, Arr and the Seven C's
or
None. They will never find a bulb that burns as brightly as the old one.
or