Now that's an interesting question. Or 'interesting' in that it comes close to potentially spoiling all the fun in things. Still, Merlin doesn't reply... Or at least, not in a direct, appearing himself sense.

No, the answer comes in the form of a feeling, one of those moments in a dream where one simply knows that a thing is so for no particular reason nor explanation.

The only way out is to solve the mystery.

But for now, that's all it is. Doubtless Merlin could potentially do more, tighten his control of both the dream itself and the one currently within it, but he's in a good mood from being able to play with his powers again. At least at the moment.