Episode 61 of 82 was kind of a departure as we have a show centered around characters that first appeared as background characters in Season 3. And I have to speculate that from the very beginning of the season the writers knew they were going to do this show. To make us believe that Nikki and Paulo have been around for the whole show their on island flashbacks include them in several re shot scenes from each of the previous seasons. In the end they get buried alive because the survivors think they are dead when they are really just paralized by a bite from the Latrodectus Regina, a fictitious Medusa Spider.