So they simply stopped dead and sat down and waited—all except Bilbo, who popped on his ring and slipped quickly to one side. That is why, when the elves bound the dwarves in a long line, one behind the other, and counted them, they never found or counted the hobbit.
Nor did they hear or feel him trotting along well behind their torch-light as they led off their prisoners into the forest.

Chapter 9 Barrels Out of Bound