There's a wonderful book on this subject (a discipline known as textual criticism) called Misquoting Jesus: The Story Behind Who Changed the Bible and Why by Bart D. Ehrman (the James A. Gray Distinguished Professor and Chair of the Department of Religious Studies at the University of North Carolina at Chapel Hill). Before I read Ehrman's book I hadn't realized how many discrepancies there are between all the different surviving biblical manuscripts. Ehrman goes into detail about why there are so many different readings, and explains how (with a lot of detective work) to figure out which readings are probably closest to the original.
On that note, here is the final chapter of the Gospel of Mark, sans interpolation (as far as we know):
When the Sabbath was over, Mary Magdalene, and Mary the mother of James, and Salome, bought spices, so that they might come and anoint Him. Very early on the first day of the week, they came to the tomb when the sun had risen. They were saying to one another, "Who will roll away the stone for us from the entrance of the tomb?" Looking up, they saw that the stone had been rolled away, although it was extremely large. Entering the tomb, they saw a young man sitting at the right, wearing a white robe; and they were amazed. And he said to them, "Do not be amazed; you are looking for Jesus the Nazarene, who has been crucified. He has risen; He is not here; behold, here is the place where they laid Him. "But go, tell His disciples and Peter, 'He is going ahead of you to Galilee; there you will see Him, just as He told you.'" They went out and fled from the tomb, for trembling and astonishment had gripped them; and they said nothing to anyone, for they were afraid.
When read this way it becomes clear why a scribe would feel the need to tack on a proper ending. It can't possibly end like that, can it? It should be noted that some textual critics do think that verses 9-20 are in fact original, since there are few witnesses (copies) that do not contain them, and since they are quoted by church Fathers as early as the second century. Others reason that Mark is obviously incomplete without verses 9-20, but that the original ending must have been lost [ref]. Although I'm no expert in textual criticism, I rather like the way the final chapter reads in the early manuscripts. It gives it a sense of mystery and suspense. Like any good zombie story, it ends on a cliffhanger.
