[Child of the 7th Age]

My feeling is that this scene almost wrote itself, at least in terms of Frodo! Saucepan Man made reference to my comments on another thread in one of his earlier posts.

PJ altered the character of Book Frodo -- making him younger, inexperienced, and vulnerable, with only limited backbone or interior wisdom -- as early as the first film. Having made those changes, the hobbit is bound to fall prey to this kind of thing. I mean Frodo was pretty far gone by the end of TTT so the scriptwriters had to come up with something in RotK that would signify the hobbit's continuing degeneration. And a split between Sam and Frodo would certainly be that!

This scene would be unthinkable in terms of the book. Fortunately, I was forewarned about the change and could accept the logic of the movie as I actually watched in the theater.

It was harder to understand why Sam went obediently down the steps. I think it would have been closer to his character if he'd had a good sob and then went sneaking after his master! But presumably he had to find that lembas Gollum had ditched so down the stairs he went. Given the way PJ set that scene up, they probably had little option.