Continuity mistake: Towards the end of the episode, when Locke is preparing to shoot Ben, Ben starts talking about Charlotte and her team. Locke is then holding his gun in his right hand, and holding Ben with his left. As Ben is saying "Because I know what they're doing here", there is an angle change, and Locke is suddenly holding his gun with both hands.
Continuity mistake: Season 4 - The Beginning of the End - Hurley is swimming in the ocean. He sees Desmond return with the boat, and by the time he gets out of the ocean and walks over to Desmond and yells, "Where's Charlie?" his shirt is dry with sweat stains on it.
Continuity mistake: Ep. 4-12 "There's no place like home". In the first flashforward, the Oceanic representative talks to the survivors about meeting the press. As she finishes by saying, "See you on the ground", you can see baby Aaron on Kate's lap, and she is holding his left hand in hers down by his side. Cut to a close-up of Kate, and Aaron suddenly has both hands free and is holding them up to his mouth.
Continuity mistake: In the scene just after John Locke's teenage mother runs from the hospital room, the nurse converses with the grandmother. You can see her put a cigarette to her mouth with visible lipstick stains on the wrong end of the cigarette, possibly from previous takes.