Where Frodo is stabbed by Shelob's stinger, Elijah Wood was actually stabbed with a prop one. On the Extended DVD Commentary, he and Sean Astin comment that it was not only very, very painful, but had actually done damage to the point that Wood had to stay in the hospital for a couple of days. Astin (on the Commentary track) jokes that they used appendicitis as the excuse, but wonder if that event is what (ironically) caused Wood's actual episode of appendicitis later on.