[Keeper of Dol Guldur]

It was when Boromir had his mad spell and scared Frodo into leaving the Fellowship.

From a reader's standpoint, I could tell it was only going to be a momentary thing. Tolkien described the look on his face as a 'spasm'. Those usually don't last long.

Men of Gondor were true to their word. It was like watching two friends go at it, I knew it was some weird madness coming over him, and that it would pass. But Frodo certainly didn't.

Then, I opened Book 3 and the first page had "The Departure of Boromir" written on it. Unsure as to whether he was just heading to Gondor or not, I read on, and WHAM! My favorite character got arrowed to death by a band of Orcs.

It took a lot of re-reading of those scenes to fully take in exactly what happened during that frantic mess on Amon Hen.