She's speaking to him! She's like him! After a lifetime of being alone, and watching humans live in communities and forge bonds with others of their own kind, he's finally encountering what has to be another Mermaid.

He takes a breath to reply, and suddenly his chest aches, bubbles swirl out into his vision as his lungs empty and his gills... stay defiantly flat against his neck, facilitating his sudden attempt at drowning.

Wrenching himself back away from the water, Shrieky falls sideways onto the bank, retching and regurgitating the liquid which he just inhaled.