Walking on a boat is even more difficult than walking on land, and Cymbeline is no great shakes at the latter to begin with. Unfortunately, neither he nor Kerem, the court magician and Cymbeline's confidante, have been able to figure out how to apply the principles of practicable magic to alleviating princely clumsiness. So Cymbeline is clinging to the railing of the boat, watching the waves, trying to avoid having to walk anywhere.
He takes her hand again. "You could catch fire -" No, she doesn't know the words. Uuuum. He's been watching her walk apparently comfortably on cursed legs all day, but those don't spread, and he doesn't have the vocabulary for a proper fire safety lecture. "It could hurt other people," he tries. "If the fire goes anywhere but the candle," (he covered these words when he was showing her how to douse and light it) "it can - get big, grow - fire eats things."
He looks around for something to burn, then picks up the discarded match he used to light the candle in his demonstration. He shook it out before, but he relights it, then sets it on the candle tray before the flame can reach his fingers. It obligingly burns into a little line of black ash. "Not really eat. Burn. Fire burns things."
She taps the candle tray and makes the sign for this-is-a-question.
"Small candle fire can't burn this," he says, tapping the tray. "That's why it's under the candle. But fire can burn clothes, wood, paper, people, - most things. If it gets big, it can burn more things."
She wakes up early the next morning; even an hour before dawn, it's brighter in her room than it ever gets in the depths. For lack of anything better to do, she makes her way to the study (she's starting to get the hang of this walking thing) and sits down with the book of sign, refreshing her memory of everything she learned yesterday.
Cymbeline is up around dawn, and when he finds her room vacated he tries the study next. "Good morning. You can read in the dark?" he inquires.
"The sun goes down, it's dark, we sleep, the sun comes up, it's light, we can see," says Cymbeline.
"So you live deep enough -" He grabs the drawing paper, draws a deep scoop of ocean, illustrates shallow, deep, deeper, shallower - "So deep that there's no sunlight, so you can see in the dark."
"Reviewing stuff from yesterday. Good, it accomplishes nothing if I don't know the signs you use... All right." He sits down next to her, and on they go.