There was the faintest sound, just hidden under the rhythmic splash of the waves. It would have gone completely unheard by a human. And in fact, it had been, every time Chal had made their way up to the surface. That was probably why the Aquapon felt comfortable enough to express such mirth so close to land.
Unfortunately, they weren't aware that the tall, green haired one with the long ears was not just a different sort of human. They had no idea he'd be able to hear them laughing with amusement at the animated struggle, between him and the seagull. But it would die down once the tears appeared, replaced by the intense sensation of being watched.
Like someone reading a book over your shoulder, or the eyes of a predator stalking prey, it would give Henry a deep feeling of discomfort.