When Kate and Sawer play the game "I Never", the bottles they drink from change from empty to full several times.
After Sawyer buys the revolver, he parks at the "Sweet Shrimp" truck. As he exits his car, he opens the revolver and spins the cylinder. As he does so, the cylinder makes a mechanical-clicking noise. This sound is not made by this type of revolver and certainly not when the cylinder is out of the gun (disengaged from the ratchet system).
When Charlie and Hurley are burying Ethan, his chest can still be seen rising and falling.
A silver fence is visible in the top of the screen as Sawyer is knocked to the ground when he is being chased by the boar. It is visible in the top of the next shot as well as the boar is running away. These fences were used to contain the boar while filming this sequence.
After Sawyer finds his blue plastic cover taken by the boar, a cameraman can be seen moving on the right, while Sawyer walks towards the camera.
Hurley says that Charlie shot Ethan 4 times when he is talking with Sayid, but in fact he shot him 6 times.