Review 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. When
this caregiver returned with a liquid antacid. Marina drank the entire bottle,
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 antacid. And took a
mint from David, the handsome paramedic.
A sentence must have a main clause. A main clause will follow 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 present, you cannot have a main clause, the essential component in a sentence.
All you have here is a participle phrase fragment. Better luck on the next one!