[Luca had been able to get on the submarine by going with Jamie, and when he hears what the green guy is saying, he stares for a moment and blinks.]

Um...how? It seems pretty well sealed...but you should probably avoid that. There are a lot of people on here who have to breathe air.

[Luca breathes water just fine, and he doesn't mind telling someone who is clearly not human that, but...well, he's not the only one on the submarine.]