Boris Balinkoff's visits
In "The Friendly Physician," shown during season 2, Balinkoff lures the castaways to his island only to perform experiments on them (but his scheme backfires and the castaways manage to get back to their island) so they know his name and appearance etc. However, in "Ring Around Gillian," shown during season 3, he returns to the island and turns the castaways into zombie-like robots via rings and a control device. He wants to conduct a trial of robbing Fort Knox and when the "robbery" is over and he commands them to give him the "gold," everyone starts pitching coconuts at him, one of which destroys the control device, freeing them from their zombie-like states. Balinkoff jumps into his motorboat and sets off. Why didn't any of the castaways recognize him? It would have made a lot better sense had the episodes been shown in reverse order!