The opening voiceover described the message included in the Voyager probe. Senator Matheson spoke of the Voyager probe to Mulder after he summoned him to his office. The Voyager message is heard as Mulder has a close encounter (maybe) at the Arecibo observatory.
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Spookyteacher's X-Trivia

2) What was Lanny's twin's name in "Humbug?"
 

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