Continuity mistake: In the "previously, on Lost" segment, we see Locke talking to Walt and he has a cut over his right eye that is straight. We we see Locke as Siyaid is explaining about gathering electronic equipment, There is now a curve to his cut. (00:00:25 - 00:09:15)
Continuity mistake: When Libby kisses Hurley at the cliff, there is a strand of Libby's hair which you can see hanging freely over her left cheek when the camera is on Hurley. When the camera is on Libby you see the same strand pinched between their heads. Then as the camera switches back on Hurley the strand hangs freely again. It's not possible that this happened only through the force of wind as their heads are stuck together quite tightly throughout the whole kiss.
Continuity mistake: In the first minute of the episode when Sayid finds the wire on the beach, his left pant leg is not torn. When he follows the wire into the jungle, just before he trips Danielle's trap, the left leg of his pants is already torn, in exactly the place where the branch will stab him. (00:02:50)
Continuity mistake: In the scene where Eko is walking up to the church and the woman tells him if he buys a statue the money will pay for a polio vaccine for the village, he is wearing an earring in his right ear. Once inside the church talking to his brother, his is wearing the earring in his left ear.
Continuity mistake: When Miles is sent to deliver "The Package" (i.e. the dead body) to Dr. Chang, after the body is taken out of the van, Miles is seen closing the door to the back of the van. After a return from a flash forward and back to 1977, the door to the back of the van is open again.