Revealing mistake: When Jack and Kate run from the bees, they enter the cave, and when they remove their tee shirts Jack's back and sides are perfectly visible. There is not even the slightest hint of any kind of scar, on the left side of Jack's back, from the nasty cut that Kate recently sewed up with the black thread.
Revealing mistake: Sun's left earlobe has a cleft, but while Jin is still cuffed to the wreckage, Sun watches Michael head off through the trees (to cut firewood) and in this close-up it is Sun's right earlobe with the cleft. The shot is flipped.
Revealing mistake: After Jack brings some survivors back to the cave, there is a shot of Hurley turning on his CD player to listen to Willie Nelson. In the next shot of Jack, as he fills bottles with water, his large tattoo is on his right upper arm, but normally it is on his left. The shot is flipped.