When the two pirates discover Jack Sparrow in his cell one of them reaches in and grabs Jack by his neck. His arm passes into moonlight, so that we see his arm and hand are now skeletal. Jack says something to the effect of "there is a curse". This is the first hint about the pirates of the Black Pearl being Undead.

Later we discover that Jack, to our surprise, is also Undead when he passes into the moonlight in the sword fight seen with Barbarossa in the treasure cave.

Now if Jack is undead, and he is seen as such in the moonlight, back in the scene where the pirate grabs Jack by the neck in the cell, why or why did we also not see that Jack was undead?!!!

Jack should have appeared as the undead Jack we see pass in and out of the moonlight in the climactic fight scene in the treasure cave. But instead, he appears fully human, even his neck and face which are in the same moonlight as the clearly undead arm of the pirate.