Move the plot:
Flat characters—minor figures that play a supporting role in the story—are used to move the plot along, providing subtle exposition. Such characters do not undergo substantial change or growth in the course of a story. They are also known as "two-dimensional characters" or "static characters."
The subordinate clause is "unprotected animals got swept out" and the main clause is because "when waves rush in". hope u get it right ;)
