I Can't Kill Gollum, but He Doesn't Have a Weapon, and I Have a Sword

Gollum thinks Bilbo stole his ring and is going to escape. He can kill Gollum if he wants to but decides that, well, I can't kill him. And so he doesn't kill him; he just follows him. Then the ring falls off his finger and some goblins see him when he gets to the back door. So you can see this is to the trickiness of the ring, where the ring will kind of fall off at bad moments. This gives us just the slight idea that there's something weird about this ring. It seems to have almost a mind of its own.