Gilligan's body conducts electricity after he is struck by lightning with a metal bowling ball in his hand. But when The Professor tries to remove the bowling ball from Gilligan's hand, a second lightning strike makes him invisible.
Did You Know?
When Gilligan, now invisible, supposedly drinks the contents of a glass in MaryAnn's hand through a straw, it empties out, but a small hose attached to it coming out of her sleeve is clearly visible. See more
Referenced in Dazed and Confused