Revealing mistake: After Charlie receives a large gash on his forehead, from Danielle's trap, Sayid tries to seal it. When Sayid pours gunpowder in the cut, he leaves a large thick trail beside Charlie's eye and on his cheek, which he does not wipe away. There is a tight close-up of Sayid igniting the gunpowder with the flame. The gunpowder beside his eye and on his cheek should have seared his skin, but it does not. The only severe wound Charlie has later is the closed charred wound on his forehead, and though he does wipe his face back at the cave, the skin on his cheek and beside his eye are fine.
Continuity mistake: When Sayid steps into the trap, in the close-up of his feet he removes his right foot, and the left remains on the ground, inside the closing rope. However, in the next shot as he's lifted in the air, it's his right leg that is caught up in the trap.
Continuity mistake: When the entire camp is heading up to the radio tower they head up the beach with the water on their right side. After the title screen shows they are walking with the water on their left side. They are going in the opposite direction as before.
Revealing mistake: When Desmond moves the rock, Smoke-Locke and Jack fight outside the cave while an earthquake shatters everything. Watch the leaves around and you'll notice that they don't move at all, giving away the camera effect. This also happens later on when Hugo, Ben and Jack are about to fix the cave of light.
Factual error: In the flashback that reveals the phone call Michael makes to his mother about Walt, Walt is seen playing a Nintendo Gameboy Advance SP before the phone call. After the phone call, when Walt stands behind Michael, Walt tells Michael that he needs new batteries. However, The Gameboy Advance SP works with a rechargeable battery which cannot be replaced with common batteries.
Factual error: The prison Desmond is released from looks nothing like any British prison, let alone the British military prison (the "Glasshouse"), which is more of a training camp than a traditional prison. The guards wear no cap badges on their berets (all British service personnel wear cap badges) and their berets are worn almost vertically on their heads, whereas British berets are pulled hard to the right. The NCO who releases him is credited as a "master sergeant" in the episode credits - an American rank which has never been used in the British Army.
Continuity mistake: At the end of the scene in the gym of the mental hospital when Hurley and Dave talk, in the background there is a guy sitting on the floor in a yoga-like position. His exact location changes between shots, as you can tell by the ground-lines. First he sits on the red line, next to where the blue and the yellow lines cross, then he sits about 5 feet further to the right, and finally he is back exactly on the same spot as in the beginning.
Continuity mistake: When John loses his voice, he uses a pad to communicate with Charlie. He writes "I need you to stand guard" in one scene and later shows the same message to Charlie. In the second scene, although it is supposed to be the same message, guard is misspelled "gaurd."
Continuity mistake: When Sayid speaks to CIA Agent Melissa Cole after Essam's death, in the first shot the body laden stretcher is wheeled to the vehicle and the back door is opened. When Agent Cole says, "Plane ticket and walking around money," in the background the stretcher is gone and the door is closed. But when Sayid asks, "What happens to his body?" the stretcher reappears as the body is being put into the open back door.
Continuity mistake: When Sayid opens the lid of the compass to show Jack, in the close-up, all of Sayid's fingernails are short and trimmed, yet, in previous and following shots (including next episode "Special") some of his fingernails (such as the thumbs) are very long again. This occurs in many other episodes, such as "Exodus 2".