What should the fools do?

It's become an internet meme - Gandalf is about to fall down the chasm after defeating the fearsome Balrog, so cries out to his friends urging them to get away.

What exactly did he say?

Many remember it as "Run, you fools!" and are surprised to learn they might be experiencing a Mandela Effect when they learn today it's "Fly, you fools!".

This could be a mishearing - some are even claiming to hear "Flee!". The plot does involve the giant eagles carrying them away, and Gandalf thinks he is about to die, so it might be a reference to that as he does the last thing he can to help them.

What does the book say?

The book says it's "Fly", but after some study it turns out Tolkien often used the word "fly" where run would have made equal sense, much as it does as a figure of speech today, as in "sorry, got to fly".

There is a suspicion of there being different versions released where this dialog has actually been edited, for example on a director's cut. If this were the case however, that version would surely have surfaced by now, since this is one of the better known Mandela Effects.

The story ends up with the hobbits flying away from Mount Doom on the backs of giant eagles, which Gandalf would have been aware of but not able to tell them with so many Orcs and Goblins following them. So the suggestion here is he knew he was about to die and was telling them about this, but it's not referred to anywhere but by the fans of the series.

With such classic stories as The Lord of the Rings, fans read and study them much more intensely that the regular passive reader/filmgoer. It is those who are claiming it has changed, which makes this one all the more myserious.