chapter 5: how do Merry and Pippin surprise Frodo during their conversation after supper?

Eventually, his friends are forced to admit that they know much of the secrets involving Bilbo's disappearance, Gandalf's advice and the ring enabling its bearer to disappear. At first, Frodo is horrified that his friends would spy on him but in the end, he is comforted by the extent of their willingness to protect him and the sacrifices they are willing to make on his behalf in spite of their limited knowledge.