Three - one to cast the bulb into the outer darkness, and two to catch it when it falls.
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First he lies on one side, then he lies on the other.
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A centipede with a wooden leg.
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Because the chicken was on vacation.
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Climb up a tree and act like a nut
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1,000,001: One to change the bulb and 1,000,000 to rebuild civilization to the point where they need light bulbs again.
or