Continuity mistake: In Episode 2-23 Live Together, Die Alone When Mr Eko runs out of the hatch when John and Desmond are faking a lock down, you see Eko put his club in his belt right in the front of his pants. In the next scene as he passes out of the door the club is gone and then when he runs back to the door as it is closing he is holding it in his hand as he drops it and it falls under the door.
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.