An onion
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Just one, but he/she will spend hours checking for technical problems.
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1,622. One to tell the original joke, and the rest to submit give some minor variation of it! For example:
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None, because people who glow in the dark don't need light bulbs.
Note: Topical to the Chernobyl Reactor disaster of 1984.
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"Pint please, and one for the road."
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