As many as possible, and don't *ask* what they do with the old bulb.
or
Because if they flew over the bay, they'd be baygulls!
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None: they just deny that the bulb ever went out in the first place.
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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.
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Tell it a yolk.
or