[VanimaEdhel]

I would guess that Frodo woke up in a similar manner to how he woke up in Rivendell, and Gandalf, knowing Gandalf, probably responded in a similar matter. Then, Gandalf said something witty, as always, and Frodo laughed.

Gandalf would have known that Frodo could not destroy the ring on his own, but I think he would have expected it. Even Gandalf did not dare to wield it, so he could not expect that the hobbits would be completely immune to its power. I think the most important thing is that the ring was destroyed. Everyone was a bit safer now.