It's like old puzzle where a judge says "I can't be an impartial arbiter for this case, because the defendant is my son," but the judge is not
the defendant's father. What's up with that? So you think about it for a really long time, but it's actually really simple, and you figure out that the boy was adopted.
Or like the surprise ending to that movie The Others where it turns out that they're all ghosts. Since it had already been done with Sixth Sense, you were thinking that they'd never do it again, but they did.
Anyway, I think the word was "goodbye" or some syntactic equivalent, or "no" or something.