Here is the passage:
Marina, the beautiful mermaid, wanted some
tuna salad. But had a small problem since she was allergic to celery. At
Sammy’s Sub Shop, Marina hoped to find tuna salad free of this dangerous
vegetable. Flopping across the tiled floor
to the counter. Marina placed her order
and then checked her sandwich for celery. Not noticing, however, the spoiled
mayonnaise. At five o'clock that evening, Marina became violently ill with
food poisoning. When a lifeguard at the beach discovered the problem, he
called 911. Even though the mermaid had fishy breath. A handsome paramedic
gave her mouth-to-mouth resuscitation. Wailing like a sick dog, the ambulance
sped off to the hospital. Where the doctor on call refused to treat a sea
creature with a scaly tail. A kind nurse, however, had more sympathy. After
she found some Pepto-Bismol. Marina drank the entire bottle of pink liquid,
feeling an immediate improvement. The mermaid told the rude doctor never
to swim in the ocean. For she would order hungry sharks to bite off the
doctor's legs. While sharp-clawed crabs plucked out his eyes. Tossing her
long hair, Marina thanked the nurse for the Pepto-Bismol. And took a mint
from David, the handsome paramedic.
Good job! A fragment will not have a main clause. A main clause follows this pattern:
Subject + verb = complete thought.
In the highlighted item, the only action expressed is flopping. Because flopping ends in ing, it is a participle, not a verb. With no verb, you cannot have a main clause, the essential component of a sentence.
All that you have here is a participle phrase fragment.