Native English speakers, could you please help me with these issues?

Laughter is always in the singular.

Surroundings is always treated as a plural.  It is the area that surrounds the focus of attention.  Sometimes it is conceptual, such as, "His surroundings as a boy shaped the man," meaning that the social group the man was raised in shaped the way he thinks.

"...by the surroundings." makes no sense at all in English.  One cannot be "by" surroundings, only in them, so if the girl and the dolphin are by something, such as cliffs or a beach, then that something has to be named.