S5·E23 The Beeping Rock

A wild story told by an 11-year-old about his recent trip to the moon enthralls Eb and Lisa. Oliver believes none of it, especially when the kid sells Lisa a "moon rock" for $14. But once the rock starts beeping under the moonlight (and when Arnold snorts at it), he suspects he's the subject of a practical joke. Oliver ships it off to NASA for their scientists to examine.