Serenity had noticed Matt's instant mood shift when she'd mentioned going back to their world. She knew that he had doubts about Poseidon's words, but didn't realize how strong they were, or how badly Medeva's words had gotten to him.
When she was going off on them, the Siren Queen had said; "Do you remember how we left our world? Drowning! Dying! What do you think will happen when we 'save the Aquarians'? We Still Die!"
Her words had been rattling around in his head ever since. Eating away at his resolve to save the Aquarians. To be honest, it was getting hard for Matt to care about what happened to them..
"Isn't this fun?! I wish we could dance-well, I could dance. I know you don't like to.. Unless we're in the water," Serenity's eyes shined from the light cast by the bonfire.