To get to the baaaaarber shop
or
A screwdriver.
or
There are footprints in the butter.
or
They're both plastic and little boys turn them on.
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