Three - one to cast the bulb into the outer darkness, and two to catch it when it falls.
or
Three. One to climb the ladder while the second kicks the ladder out from under her. And the third to say, "I knew that was too high for you dear."
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Because there's no one else to wag it for him.
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Because E.T. eventually went home!
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An embarrased mime!
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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:
or