There's an interesting thing that happens in Peter Jackson's adaptation of Lord of the Rings: Fellowship of the Ring that subtly illustrates how small changes from the source material can change the entire meaning of a scene and what follows it. It's the scene in which Gandalf officially learns that Bilbo has a magical ring that may, or may not be, but probably is, evil.

First off, let's visit the passage as written by J.R.R. Tolkien. So Sin 1 for this post is "Reading." But I assume you like to read if you're here, so here's the passage:

'No don't give the ring to me,' said Gandalf. 'Put it on the mantelpiece. It will be safe enough there, till Frodo comes. I shall wait for him.'

Bilbo took out the envelope, but just as he was about to set it by the clock, his hand jerked back, and the packet fell on the floor. Before he could pick it up, the wizard stooped and seized it and set it in its place. A spasm of anger passed swiftly over the hobbit's face again. Suddenly it gave way to a look of relief and a laugh.

Now we skip ahead, after Frodo and Gandalf have a discussion at length about the ring, Gandalf being cautious, trying to find out what Frodo knows without divulging his suspicions. Frodo says:

'You are very mysterious! What are you afraid of!'

'I am not certain, so I will say no more. I may be able to tell you something when I come back. I am going off at once: so this is good-bye for the present.' He got up.

In the movie, it goes down like this: