How is Bilbo caught by the trolls?

During a strong rain storm, the group loses a large amount of food, and a pony gets frightened and jumps into the water.  Bilbo is sent to investigate a light on the side of the road, and he finds three trolls sitting by a fire. Bilbo is caught trying to pick one of their pockets, but later escapes into the woods when the trolls begin to argue. The rest of the dwarves are captured as they approach the fire. Gandalf uses magic to get the trolls to argue with one another. They are so lost in their argument, that they don't realize when it is daylight, and they eventually turn into stone.